DESCRIPTIONS OF SPECIES.
The known foraminiferal representation of the Guadalupian is meager compared with that of some regions to which reference will be made. It comprises only nine species, distributed as follows:
Fusulina elongata is large and abundant, while the other types are much smaller and much more rare, so much so in fact that except a couple of silicified examples of Fusulinella none have been seen macroscopically. They occur, where noted, here and there in thin sections. In this condition, owing to the small number of observations, the fortuitous orientation in which they appear, the generally altered or obscured microscopic structure, and, I may add, my own too slight familiarity with the group, I have been able to determine their generic relations only somewhat unsatisfactorily, and have identified them specifically not at all. Persistent effort in sectioning would probably bring to light many other forms and lead to a more exact determination of them, but I am fain to believe that Foraminifera, aside from Fusulina, are considerably less abundant in the Guadalupian than in some other Carboniferous faunas.
For the Foraminifera, somewhat at variance with the scheme adopted for other groups, I have not introduced any family headings, as I find that the authorities who have been consulted disagree very widely in their family groupings and I am myself unable to determine the matter on its merits.
In the Salt Range of India Schwager found four species of Fusulina, one of Fusulinella, one of Lingulina, one of Involutina, and one of Margaritina. Among the Fusulinas there is nothing to compare with F. elongata of the Guadalupian, and it will thus be seen that the two faunas show very little relation to one another in this particular at least.
From China and Japan (in Richthofen's China) Schwager cites a still more extensive and varied fauna, consisting of 15 Species, representing 8 genera, as follows:
Here again there is nothing to compare with Fusulina elongata, and the whole fauna has a different complexion from the Guadalupian, though, as I have before remarked, a more perfect knowledge of the Guadalupian Foraminifera is likely to increase its generic resemblances, at least, to the other more abundant faunas. Lörenthey also records an extensive protozoan fauna from China. He obtained the following types:
This fauna, which comprises 14 genera and 31 species, is of course much more extensive than the Guadalupian. Most of the Guadalupian genera, however, are found among those cited by Lörenthey. Among the non-Guadalupian genera especial importance attaches to Schwagerina.
The Indian Archipelago has furnished but a small record, one or two species of Fusulina, Moellerina, and Schwagerina being all that I have encountered.
In Möller's monograph on the Russian Foraminifera no fewer than 43 species are discriminated, representing the following genera:
Already in the Moskovian this group was fairly abundant. Trautschold cites the following:
Möller also names the following genera from the "Lower Carboniferous," which I take to be a corresponding horizon:
They are, perhaps, especially abundant in the Gschelian, where one genus is regarded as a diagnostic fossil, the Schwagerina zone being named after it. It is of importance to note that Schwagerina is not known in the Guadalupian series. Where it does occur in western North America, its horizon is, so far as can be determined, lower and its associated fauna different. If it occurs in the trans-Pecos section, as is very likely, its position is in the Hueco, below the Guadalupian.
To return to the Russian section, the number of species in the Artinskian is still considerable. Möller cited only Fusulina verneuili and Schwagerina princeps, but Stuckenberg records Fusulina verneuili, F. cf. longissima, together with two undetermined species of the same genus, as well as Cribrostomum gracile and C. cf. commune. Krotow is authority for the occurrence at this horizon of Cribrostomum gracile, Cribrostomum sp., Fusulina verneuili, Fusulina 3 sp., and Schwagerina princeps.
In the Russian Permian the class is still present in force, for although other authors give but scanty mention, Netschajew records four species of Nodosaria, one species of Endothyra?, one species of Cribrostomum?, and two species of Spirillina.
Enderle cites from Balia Maaden, in Asia Minor (as identified by Schellwien):
I do not know whether Gemmellaro described any Foraminifera from the Fusulina limestone of Palermo, but this name indicates that the genus Fusulina, at least, was abundant. Schellwien described a very considerable foraminiferal fauna from the Carnic Alps, of which the following is a summary:
Gortani also found forms belonging to this group in the Carnic Alps, to wit:
The German Dyas is not without this class of organisms, Geinitz citing them under the following genera:
In the Permian of England, King cites three species of Dentalina, two of Textularia, and one of Spirillina. Bradya quotes four species of Trochammina, one species of Nodosinella, one species of Nodosaria, two species of Dentalina, and two species of Textularia from this horizon. He also cites distribution for other areas, his entire work involving 62 species and 20 genera; but as he excludes the Fusulinas, and as the Permian horizon is that which chiefly interests this discussion, it does not seem necessary to consider his other data.
I have not found recorded any representatives of this class from the Arctic region, from New South Wales, or from South America.
The survey of the foraminiferal development of the upper horizons of the Carboniferous, thus hastily made, seems to bring out several facts of at least seeming significance. The different types aside from Fusulina can not positively be said to be less well represented, rather than less well known, in the Guadalupian, but I believe that they really are less well represented than in certain favored areas in other parts of the world. Fusulina elongata, the characteristic Guadalupian foraminifer, is unique the world over for its robust growth and elongate shape. The conditions which proved so salubrious for Fusulina may have been adverse to the development of other types, so that they are, as already noted, somewhat scarce. In the typical Russian Permian, the Dyas of Germany, and the Permian of England, while other foraminiferal types persist the genus Fusulina is made notable by its absence. It is represented in the Artinsk by two species, F. verneuili and F. longissima. These two Russian species, together with several from India, where F. longissima is also found, are especially similar to F. elongata by reason of their long slender shape, a configuration which seems to be rather significant of late Carboniferous horizons, of a faunal province, or of both.
If references in literature furnished an accurate index of the distribution of fossils, one would be justified in inferring that except for the fusulinoids Foraminifera were much less numerous and well differentiated in the Carboniferous of North America than in other parts of the world, since there have been obtained in England, in continental Europe, in India, and in China a large number of genera, such as Fusulinella, Stacheia, Psammophis, Hemidiscus, Archæodiscus, Spirillina, Nodosinella, Lingulina, Climacammina, Bradyina, Cribrospira, Cribrostomum, Moellerina, and others, which are as yet unknown in the two American continents.
Compared with this list our own representation is meager indeed, including little besides the fusulinoids. Endothyra is plentiful at certain localities in the typical Mississippian, and a species has also been cited from probably the same general horizon in the Rocky Mountains. Bagg, furthermore, has given a list of genera not, for the most part, recorded elsewhere, observed in a Mississippian limestone of Colorado.a A species of Nodosinella has been also described from the Carboniferous limestone of Windsor, Nova Scotia, but these occurrences are also, so far as known, in the lower Carboniferous.
In the upper Carboniferous we have five species of Valvulina from the Mississippi Valley, which have never been rediscovered since their first description, and the following list, which Spandelb has recently described from the Pennsylvanian of Kansas: Ammodiscus cf. filum, Ammodiscus concavus, Bigenerina cf. eximia, Monogeneria atava, Monogenerina nodosariiformis, Textularia gibbosa, Tetraxis conica var. lata, Nodosaria postcarbonica, Geinitzina postcarbonica, Dentalina bradyi, Fusulina cf. regularis,c and Fusulina sp. There are, in addition, the Fusulinas, which are so abundant that they occur almost everywhere. In this general reference are also included fossils of the genus Schwagerina which are found only in the far western areas of this continent, so that the foraminiferal representation of the typical Pennsylvanian with these few exceptions is restricted, one might almost say, to the genus Fusulina itself. But the Fusulinas of the Mississippi Valley for the most part belong to a single type, for which I recently introduced the name Triticites. Triticites ranges well westward, but the typical Fusulinas with fluted walls appear to be rare in the Pennsylvanian and so-called Permian of the Mississippi Valley.a
If one compares the foraminiferal fauna of the Guadalupian with that of the Pennsylvanian the greatest difference is apparent. Not only does the Guadalupian contain a larger and more varied representation, but where there is common ground the differences are really remarkable. Fusulina elongata both belongs to a different and more complex group of the fusulinoids than Triticites secalicus, and is even unique among the Fusulinas themselves.
When fossils strike the eye they are collected, and when collected they are described; but they escape observation not only by reason of rarity but by smallness of size as well, and the Fusulinas owe their frequent citation to excellence in both particulars, since, though smaller than most fossils, they are readily visible as individuals, and in many places they occur in incalculable profusion. The other types are, for the most part, of less robust proportions, and while they might thus more readily escape observation and owing to difficulty be neglected in research, it is pretty safe to conclude that they are really far less plentiful than the Fusulinas. Therefore it is probable that a well-directed and persistent search would show that the Pennsylvanian foraminiferal fauna was fully as diversified as the Guadalupian, and that the Guadalupian itself was much more varied and extensive than we now know it.
Thus while it is likely that the Foraminifera of the Guadalupian are really no more varied than those of the Pennsylvanian, I can not but lay stress on the great difference manifested by the single type which they possess in common, and express the expectation that, in view of this difference and that of the associated fauna, the remaining Guadalupian and Pennsylvanian Foraminifera, when they shall have become better known, will prove to be almost equally distinct.
Although the true Fusulinas, of which F. elongata is a representative, occur in western North America, they are quite distinct from the latter specifically and are, so far as known, associated with very different faunas. The only exception which need be made to this statement is a large elongate species occurring in the highest Paleozoic rocks of California, which, though I have not examined it microscopically, by its shape and size is very suggestive of F. elongata. The associated fauna, however, contains little that recalls the Guadalupian.
Schwagerina, at least the large rotund type, appears to be restricted to the western portion of the continent, its horizon in California being below the elongate Fusulina just mentioned. This genus is not known in the Guadalupian fauna, its position in the trans-Pecos sectionif it really occurs there, which I can not positively assertbeing in the Hueco formation, which lies below the Guadalupian beds.
Genus FUSULINA Fischer de Waldheim.
This genus is represented in the Guadalupian fauna, so far as known, by but one species, that described by Shumard nearly fifty years ago as Fusulina elongata; but while apparently possessing the structural characters of typical Fusulina, F. elongata is unique among known members of the genus in the relatively gigantic proportions which it attains. It is found in the profusion in which shells of this class are wont to occur, whole strata being practically composed of it.
It has this abundance in the highest known horizon of the Capitan limestone, where, with the exception of sponges, it dominates the faunal representation to the exclusion of other types.a It is absent in the middle portion of the Capitan, however, where the most prolific molluscan fauna was found. In the "dark limestone" and in other portions of the Delaware Mountain formation it is also abundant, associated with trilobites, mollusks, etc. It is not known in the black limestone at the base of the Guadalupe section, however, but has been obtained from the southern Delawares and probably from the Glass Mountains.
Although, as before remarked, but one species has at present been discriminated in all this wide range and distribution, it is possible that local conditions of preservation may have operated to conceal the presence of related forms, although unrelated species, unless very rare, probably do not occur. In the Guadalupe Mountains these fossils are not found free and with the detailed characters brought out by weathering. On the contrary, at some horizons, before they were covered over and solidified into the hard Capitan limestone, each organism became the center of a thick dolomitic envelope, which effectually conceals everything except general proportions. Thus, for the most part, instead of using macroscopic characters for the index of specific discrimination, this has to be reached much more laboriously by thin sections of individuals selected more or less at random. While, as already stated, similar species may from these causes have been passed over, obviously distinct ones, such as have a notable difference of proportion, must be absent or rare.
F. elongata possesses the structures of typical Fusulina, but differs importantly from the Pennsylvanian forms, which commonly pass as representatives of this genus. This fact led me to introduce the term Triticites b for the Pennsylvanian type. While in Fusulina the radial walls are so fluted as to form with one another a division of each longitudinal chamber into a great number of little chamberlets, in Triticites the radial walls are straight, except in the terminal regions, and the chambers practically continuous from end to end. All the structural features which I noted in Triticites had already been described by Schellwien for Fusulina,c and the main differential character lies in the plication of the radial walls. Although Doctor Schellwien writes me that, as I had already surmised, an intergradation is found between these two types, and expresses the opinion that Triticites on this account is not a valid term, I venture to hold to the belief, having due regard to his extensive knowledge of this group, that where the extremes are as widely divergent as in the present case they should not be placed in a single genus. A distinguishing name will do good service in recording differences, both in dispersion and geologic range.
FUSULINA ELONGATA Shumard.
1858. Fusulina elongata. Shumard, Trans. Acad. Sci. St. Louis, vol. 1, p. 297 (date of volume, 1860). White [Permian] limestone, dark limestone, and sandstone: Guadalupe Mountains, New Mexico and Texas.
1859. Fusulina elongata. Shumard, idem, p. 388.
White [Permian] limestone and underlying sandstone: Texas and New Mexico.
Shell nearly cylindrical, very slender and much elongated, pointed at the extremities, which are slightly curved; chambers very numerous; aperture very narrow, linear, extending the entire length. Surface covered with fine, somewhat flexuous striæ.
Dimensions.Length, from 1 to 2 inches; width, from 1 to 2 lines. This species is at once distinguished from F. cylindrica by its remarkable length.
Occurs in the white limestone, dark limestone, and sandstone of the Guadalupe Mountains of New Mexico and Texas.
Shumard's rather brief characterization of this species, which is quoted above in full, leaves considerable to be added in the way of detail and somewhat in the way of correction. Probably the most remarkable feature of F. elongata is its length and slender proportions. Shumard gives the length as from 1 to 2 inches (25 to 50 mm.), and the width as 1 to 2 lines. About 5 mm. is the maximum diameter observed by me, and the average is perhaps 3 to 3-1/2 mm., while many examples are still smaller. I also, in a brief preliminary announcement of this fauna, said that Fusulina elongata probably attained a length of 2 inches. This is perhaps an overestimate, as no specimens have come to hand exhibiting these dimensions. These fossils show an unexpected tendency to break up into short sections, and also to exfoliate spirally. This is especially true of examples from the Delaware Mountain formation and from the "dark limestone," where probably the largest individuals occur. It is rare to find specimens complete, even in the matrix, at these lower horizons, and I have never seen one of the larger specimens complete. Fragments measuring 30 mm. are rare. One is, moreover, liable to be misled in estimating the original length from fragments, for, instead of tapering gradually to a point, many examples, especially large ones, terminate rather abruptly with bluntly rounded ends. It seems to me not improbable, however, that some large examples did reach nearly to the dimensions indicated50 mm.
The shape is usually more or less contorted, sometimes once curved, less often in several directions. The sutures are as a rule flexuous, and sometimes their course is very irregular. They are also occasionally confluent, in which case of course the chambers do not extend the entire length of the shell. The sutures are somewhat depressed and are closely disposed. They number 36 to 39 in a large volution, as indicated by the partitions seen in transverse sections. In addition to the longitudinal markings produced by the sutures there are also to be clearly seen in some specimens transverse rings, which are close together and are undoubtedly to be associated with the division of the chambers into chamberlets. The number of volutions in this species is uncertain, and of course varies in proportion to size. It is difficult if not impossible to count those in the extreme center. Certainly ten or eleven turns are completed in some instances.
Although several authors, more recently Schellwien in particular, have described the structural features of Fusulina with much care, some observations on the structure of F. elongata seem in this connection deserving of record. The initial cell is well shown in a number of the sections studied and is of unusually large size. What may be regarded as the mature condition seems to have existed during the formation of most of the shell. Growth was effected by the addition of chambers extending usually from end to end of the axis. The back and floor of each chamber are formed by earlier portions of the test, the top and front by a new mural growth which at first has a spiral direction and later by a sudden bend becomes radial. Thus what superficially in cross sections has the appearance of a continuous revolving wall, and has sometimes been represented as such, is in reality made up of many discrete sections, each of which is directly connected with a radial partition. Neither the spiral nor the radial walls which constitute the two structural elements are simple or continuous as a whole. They are mutually continuous, but are discriminated by a change in structure accompanying a change in direction. Almost always it is possible to make out, and in most cases to do so clearly, an outer layer, which is thin and opaque, and an inner portion, quite distinct from the crystalline calcite that usually fills the chambers, which is translucent and relatively much thicker. That the dark line which bounds the outer half of each chamber does not simply mark a plane against which organic material was deposited from two directions is shown by the fact that it defines the outline of the final volutions. It is true, however, that on the inner volutions secondary deposits of testaceous material are sometimes made. This layer forms a plane of dehiscence along which the volutions separate, but it remains with the older volution of which it formed the external surface.
There is also a structure which has caused the shell in this genus to be described as perforate. In brief, the wall seems to be intersected by innumerable tubular pores, or if solid by rods, whose direction is normal to the two surfaces. As these have the same appearance in sections perpendicular to the axis as in those parallel to it, they can safely be said to be cylindrical, though, as they can often be distinctly seen to contract toward the outer side of the wall, their real shape is rather that of an elongated cone. They are dark when seen in section, like the outer superficial layer with which they appear to connect. This circumstance, together with the fact that they are evidently not continuous with or of the same substance as the crystalline calcite with which the chamberlets are filled, leads me to doubt that they were ever hollow tubes. This structure seems to be limited to the revolving wall, the radial wall being solid and homogeneous.
Just after the wall is flexed from a spiral to a radial direction it becomes regularly and strongly fluted transversely to its length. Each of the partitions is so arranged with regard to those adjacent that the concave folds of the one are opposite and adnate to the convex folds of the other, so that each long longitudinal chamber is in this way cut up into many chamberlets. It is the absence of this structure in Triticites which distinguishes that genus from Fusulina. Practically no intimation of this structure is retained upon the exterior, where a straight, linear, longitudinal furrow marks the suture between each two chamberlets; but if the outer wall is removed the anastomosing partition walls are seen forming a regular network whose openings have a quincuncial arrangement and extend in spiral lines. Almost equally marked evidence of the same structure can often be seen at the aperture in the columnlike fluting of the partition wall. Indications less striking appear in sections in the loops and lines which the partitions make when cut in different directions.
Probably no single chamber is completely inclosed by its partition wall, which many sections, both in Triticites and Fusulina itself, show to be incompletethat is, it is seen not to extend quite to the revolving wall beneath. In a transverse section the partitions appear to be sometimes complete and sometimes incomplete, and as it often happens that for a whole volution or two they are the one, and then for an equal distance the other, it seems rather probable that little openings are left at the base of the partition wall, and that these are somewhat regular in their distribution, appearing more or less consecutively in a linear way in concentric lines. It was through these openings, and not probably through the pores, that the protoplasm issued to feed and to secrete new chambers.
Shumard cites the range of this species as being extended from the yellow sandstone though the "dark limestone" and into the "white limestone" above. This statement is corroborated by later observations, and I have not been able to discriminate specifically between the lowest and the highest occurrences of this form. While maintaining about the same proportions throughout this range it is possible that a discrimination can be effected on certain microscopic differences. For example, in cross section the specimen from the Delaware Mountain formation represented by fig. 8 of Pl. XXII shows the shell to be more loosely coiled; or, in other terms, the quotient of revolution to be different from that found in figures of specimens from the "dark limestone" and from the top of the Capitan formation. My studies have not yet progressed sufficiently for me to state whether this difference is constant between forms occurring at the two horizons, or whether it can possibly come within the limits of specific variation.
Fusulina elongata is frequently found in extreme abundance. Calcareous bands are produced in the sandstone by its occurrence, and thick strata in the limestones are composed almost entirely of it. It is especially abundant in the very highest strata seen in the Capitan formation,a where the fauna seems to consist almost wholly of these Fusulinas and of calcareous sponges. At this horizon, where considerable beds are almost entirely made up of these organisms they show a marked tendency to assume uniform orientation, as if arranged by current action, so that when the rock is broken in one way only transverse sections are exposed, and in another only longitudinal.
Near the base of the Capitan, in what is probably Shumard's "dark limestone," they are again very abundant, but are here associated with a considerable brachiopod fauna. The main Guadalupian fauna described in these pages, which was obtained about midway between these two horizons, is not associated with Fusulina. In the Delaware Mountain sandstone these fossils occur at several horizons in great abundance, but they have not yet been found in the basal black limestone.
In addition to localities in the immediate vicinity of Capitan Peak we have Fusulina elongata from points many miles to the south, where it occurs in limestones supposed to represent the Delaware Mountain sandstone of the typical Guadalupian section, as well as from the same horizon (provisionally) far to the southeast, near Marathon. A large, much elongated, and slender species, probably identical with this, is found in great profusion in California, on McCloud River, in the upper beds of the Carboniferous section above the McCloud limestone, which carries Omphalotrochus and Schwagerinai. e., in the Nosoni formation, or, as it was formerly called, the McCloud shalesand also in other areas.
Horizon and locality.Top of Capitan formation, Capitan Peak (stations 2905, 2966, 3762); "dark limestone," station 3762a, Pine Spring (station 2930), and hill southwest of Guadalupe Point (station 2924); Delaware Mountain formation, Guadalupe Point (stations 2903, 2919, 2931, and 2963), Guadalupe Mountains, Texas. Delaware Mountain formation, southern Delaware Mountains, Texas (stations 3500, 2969, 2957, and 2964). Delaware Mountain formation, Comanche Canyon, Glass Mountains (station 3763) and mountains northwest of Marathon (station 3840), Texas.
Genus FUSULINELLA Möller.
FUSULINELLA sp. a.
Pl. V, fig. 6.
Although much less abundant than the Fusulinas, the Foraminifera belonging to other genera hardly form a negligible quantity in the Guadalupian fauna. For the sake of completeness I have felt constrained to give them a cursory treatment, although with much diffidence. On the one hand, I have not had previous occasion to give these forms much attention, and consequently approach the subject with but little experience; and, on the other, the study of the Guadalupian Foraminifera is beset with something more than the ordinary difficulties. Though the Fusulinas occur in great profusion, I have been unable to find the other forms in the gross, owing to their small size and much less abundance, and it is necessary both to discover and to study them by aid of thin sections. This means, of course that no examination can be made of their external characters and that the orientation of the sections is entirely a matter of chance. Furthermore, in most cases the original substance of these organisms has been so altered that the detail of their structure has been impaired if not altogether obscured.
Although, as I have said, they are very much less numerous than the prevailing Fusulina elongata, as also very much smaller, a number of organisms of foraminiferal nature are shown in the sections which I have had made; but for the most part the few cells are arranged in so irregular a manner that the sections evidently depart widely from the critical orientations in respect to which the structure of the organism can be intelligently studied. I regard it as possible, therefore, that the sections examined really represent a more varied foraminiferal development than I have been able to discriminate; and, on the other hand, that some of the forms discriminated may really be one and the same.
In the highest horizon of the Guadalupe Mountains, associated with Fusulina elongata, though much less abundant, is a form which I think should be referred to Fusulinella. One section especially shows a regularity of arrangement indicating that it is oriented in accordance with one of the axes. It is represented by fig. 6 of Pl. V. It seems to be directed at right angles to the axis of revolution and to be situated rather near one of the ends. Other sections which can probably be referred to the same species appear to have cut the shell more at random. The general shape of the organism, so far as can be ascertained from my very imperfect data, was spheroidal, much flattened through the axis. There are about 24 chambers in the final volution, as near as can be counted. The walls appear to be double and imperforate, but the minute structure of many of these forms has been obscured or even perverted by preservation. These characters seem to warrant the provisional assignment of this shell to Fusulinella, but my material is too imperfect to justify me in describing it as new or attempting to identify it with species known.
Horizon and locality.Top of Capitan formation, Capitan Peak (station 2905); Delaware Mountain formation, Guadalupe Point (station 2903), Guadalupe Mountains, Texas. Delaware Mountain formation, southern Delaware Mountains, Texas (station 2957).
FUSULINELLA sp. b.
Pl. XXVII, figs. 5 and 5a.
This species is represented by a single silicified specimen from the southern Delawares. Only the exterior is accordingly known. The shape is compressed spherical, the axial diameter being about half that in the plane of revolution. The latter measures about 1-3/4 mm. There are, as well as can be counted, 26 chambers in the last volution. The partitions are simple and straight. Either the sutures are very deep or, more probably, what is presented for study is not the shell itself but a silicified mold of the interior, and what appear to be the sutures are really the cavities left by the walls.
There are no American species with which to compare this form save Fusulinella sp. a of the Capitan, and as the present form is known only macroscopically and Fusulinella sp. a only in thin sections, which are, moreover, for the most part oriented at random and have the structures but poorly shown, the conditions are not at hand for a very satisfactory comparison. The present form appears to demand recognition as a distinct species because it is much larger and has, for the size, less numerous chambers.
It hardly seems profitable to compare with foreign species the form under discussion, because the conditions under which it is studied would prevent a satisfactory conclusion in any event.
Horizon and locality.Delaware Mountain formation, southern Delaware Mountains, Texas (station 2969).
FUSULINELLA sp. c.
This species, like the foregoing, is represented by a single specimen and, though found in association with it, appears to belong to a distinct species, or at all events a distinct variety. The number of chambers and other characters are about the same in both, the only obvious difference being that of proportion, the present form having about twice the axial diameter of the other, resulting in a nearly spherical, instead of a flattened, shape. Owing to their size and shape it seemed probable that this and the preceding form were Fusulinellas rather than Schwagerinas, it being impossible to resort to thin sections for the determination of this point.
Horizon and locality.Delaware Mountain formation, southern Delaware Mountains, Texas (station 2969).
Genus ENDOTHYRA Phillips.
ENDOTHYRA sp. a.
Pl. XVII, fig. 11.
One of my slides shows a shell referred with some doubt to the genus Endothyra. The section does not pass through the test with a critical orientation, but somewhat obliquely. For a short distance it nearly coincides with the plane of one of the partitions, probably the outer partition, and partially shows an interesting feature, namely, that this wall was pierced by relatively large round pores. How many of these there were and whether they had any definite arrangement are at present unanswerable questions. They appear to have been few.
The obliquity of the section which enables this character to be seen distorts the remaining parts so that the facts that would be shown in a section normal to the center of the axis can not be definitely ascertained. There must have been from 15 to 20 chambers in the last volution, and the partitions can be inferred to be strongly convex. As so often occurs in the Guadalupian rocks, the original composition of the shell seems to have been altered and the present appearance can not be entirely trusted. There is a thin dark-colored outer layer and a thicker, less dense inner one which shows very indistinct traces of having been perforate.
The appearance of this section is shown by my figure. The general character seems to agree best with Endothyra. The number of chambers is perhaps a little high for that genus, and much too high for Bradyina or Cribrospira. The important feature presented by the perforated outer partition is, to be sure, rare in Endothyra. Möller has found it in a few species, where it seems to occur chiefly in the final chambers when they assume a rectilinear instead of the usual spiral direction. It is much more common in Bradyina and Cribrospira, but so far as can be inferred the pores are larger and less numerous in the form under consideration than is characteristic of those genera.
Horizon and locality.Top of Capitan formation, Capitan Peak (stations 2905?, 3762); "dark limestone," Pine Spring (station 2930), Guadalupe Mountains, Texas.
ENDOTHYRA sp. b.
Pl. XVII, fig. 10.
My figure shows the appearance of the form on which the present division is based. I judge that the section is not quite perpendicular to the axis and that it lies a little to one side of the center. Some of the partitions are incomplete and some appear to be complete. The line of growth in the final volution of the shell seems about to be changing from a spiral to a rectilinear direction, a feature sometimes found in Endothyra but rare in other genera. The final volution appears to have consisted of about 18 chambers.
The microscopic structure is obscure, but appears in the main to be like that of the foregoing species, with a thin dark outer and a thick light inner layer, but in places the walls seem to be divided by a line of nearly transparent material, so that they have the semblance of being double, as was described by Möller for Fusulinella and as is seen in the figured specimen of Fusulinella sp. a. To this fact but little weight can attach, as owing to alteration a similar appearance can occasionally be noted in Fusulina elongata, and as Schellwien regards this apparent structure to be adventitious even in typical Fusulinella. Indeed, the discrimination between Fusulinella sp. a and these two species of Endothyra rests on uncertain evidence. The figured specimens of the Endothyras have of course peculiar characters, which are not to be found in the other sections referred to the same species. These differ from Fusulinella sp. a in being larger and having, for their size, fewer chambers. But if the figured section of Fusulinella sp. a were supposed to be taken near an extremity of the axis, a section through its center would give at the same time a larger size and no greater number of chambers. Such a section would present no marked differences, so far as I can see, from most of those referred to Endothyra sp. a and Endothyra sp. b without, however, necessarily possessing the peculiar features of what may be called the typical specimens of either. But unless situated at the very extremity of the axis, and unless very nicely oriented to it, the figured section of Fusulinella sp. a could hardly fail to cut some of the earlier volutions and consequently to present a different appearance from what is really the case. It seems probable, therefore, that the forms placed with Fusulinella sp. a are different even from the nontypical shells referred to Endothyra, being neither peculiarly located sections nor small and immature specimens. As the number of chambers per volution increases with size, in the latter event the number in mature shells of the Fusulinella would be greater than in the corresponding size of the Endothyra.
If really congeneric with the types, the other specimens referred to Endothyra sp. a and Endothyra sp. b can hardly be Fusulinellas, even if they prove not to belong properly to Endothyra; while if not congeneric they may be Fusulinellas, but they are as distinct from Fusulinella sp. b as from Fusulinella sp. a, being much smaller and for the same size more highly chambered.
Horizon and locality."Dark limestone," Pine Spring, Guadalupe Mountains, Texas (station 2930).
ENDOTHYRA sp. c.
Pl. XXVII, fig. 4.
Unlike the two other types which I have referred to this genus, that under consideration is represented by a section which is nearly parallel with, instead of nearly perpendicular to, the axis. I have not thought it to be the same species as they, however, because it is much smaller and composed of a larger number of cells than they would have had at the same size. The general character of this form is shown by my figure, to which I am unprepared to give any additional data.
The other species were referred to Endothyra with some doubt, but the appearance of the present section is more characteristic and the generic reference is made with greater confidence.
While the four different types of coiled shells which I have discriminated as Fusulinella sp., Endothyra sp. a, Endothyra sp. b, and Endothyra sp. c are quite distinct in the oriented sections on which they are based and in some others, the many views fortuitously cutting these organisms present, naturally, very varied appearances, and many of them I find it impossible to refer with any confidence to one type or the other. Of such assistance as might be afforded by the minute structure of the test I have been deprived, as the structure has in most cases been lost through alteration.
Horizon and locality.Delaware Mountain formation, southern Delaware Mountains, Texas (station 2964).
Genus SPIRILLINA Ehrenberg.
SPIRILLINA aff. S. PLANA Möller.
Pl. XVII, fig. 9.
This species is based essentially on the little specimen a section through which is shown by fig. 9 of Pl. XVII. It appears to be related to S. plana Möller, but to be probably a distinct species. The rate of expansion is considerably less than in Möller's species, the walls relatively thinner, and the number of volutions greater. The walls do not show the closely perforate structure represented in Möller's figure, appearing in fact to be nearly structureless, but this is probably the effect of alteration. I am not certain that my specimens do not belong to the group for which Schellwien recently introduced the name Hemidiscus.
Because my material is so limited and its characters so imperfectly known I have, as in other cases, refrained from proposing a specific term for this form.
Horizon and locality.Top of Capitan formation, Capitan Peak (station 2905); "dark limestone," Pine Spring (station 2930), Guadalupe Mountains, Texas.
Genus LINGULINA D'Orbigny.
Pl. XXVII, fig. 3.
The figure on Pl. XXVII shows all that is known of this form, which occurs, however, in several slides from this station. It appears to consist of a rectilinear series of flattened, subspherical, more or less embracing chambers, which gradually increase in size from one end to the other. The microscopic structure has been entirely obscured, and the section does not show whether the chambers were connected by large oral apertures. The general appearance is rather suggestive of Lingulina széhenyii Lörenthey,a but the generic and the specific relations are at present a matter of uncertainty.
Horizon and locality.Delaware Mountain formation, southern Delaware Mountains, Texas (station 2964).
Last Updated: 05-Dec-2008