siderably after the nodes have begun to show themselves two sulei are gradually introduced upon either side, dividing the external portions of the volutions into three approximately equal divisions. The area between the umbilicus and the sulcus on each side is occupied by the nodes or plications, which die out as such toward the sulcus, bending sharply and strongly forward in so doing. At this point they degenerate into or are replaced by growth lines, which are continued across the ventral surface defined by the two sulci. Here these sharp growth lines have a deeply concave direction, so that the aperture shows a deep hyponomic sinus defined by two strongly projecting points, whose situation is marked by the two sulci. (See fig. 15a of Pl. XI.)

The internal sutures have not been determined. The external ones show the general characters of Glyphoceras. There is a low siphonal saddle, which is sharply indented on top. The two lateral saddles are both rounded, the first being narrower than the second and projecting far beyond the siphonal saddle. The pair of siphonal lobes are low and narrow, the outer limb being much longer than the inner. The lateral lobe is rounded and rather large and broad.

The foregoing description, based upon the only known species. probably includes characters which will not be found without modification in related forms when such are discovered.

This is a rather well-marked type, and I hardly feel called upon to point out the obvious differences which distinguish it from other genera of the same family. From Gastrioceras, as the term is here used, it is distinguished by its discoidal shape, its radially elongated cross section, its sculpture, consisting of two revolving sulci and plications radiating from the umbilicus (though the latter feature is found in the typical section of the genus), by the shape of the aperture, by the suture, both lobes and saddles being rounded throughout, and by the absence of constrictions. Much more nearly related is it to the associated type which I have distinguished under the title Adelphoceras. The differences here are the absence of constrictions; the widely different ornamentation, resulting in part from the pecul iar shape of the aperture in the form under consideration; and the suture, the lobes being rounded in Eumorphoceras and angular in Adelphoceras.

Type.-Eumorphoceras bisulcatum.

EUMORPHOCERAS BISULCATUM n. sp.

Plate XI, figures 15-19a.

Shell small, probably attaining a diameter of 30 mm., but so far as observed usually not exceeding 10 mm. The shape is discoidal, becoming increasingly so with advancing age. Umbilicus moder

ones.

ately large, proportionately smaller in old specimens than in young The cross section varies greatly, from transverse and elliptical in the larval stages to radially elongate and elliptical at maturity. The type specimen has a diameter of 11 mm., the height of the last volution being 6 mm. and its width about 5 mm. The umbilicus measures 2.5 mm.

The surface is divided by two revolving sulci into three nearly equal portions. The areas nearest the umbilici are marked by regular, strong, angular, radiating ribs, separated by subangular channels of about the same width. Near the revolving sulci the ribs and channels are bent strongly forward, and at the same time they rapidly die out and disappear. The ventral area rises rather strongly from the two sulci, by which it is defined. Its borders are marked by an additional depressed line, which is less distinct than the main ones, in connection with which they give rise to a low revolving carina on either side. The remainder of the ventral surface is marked only by growth lines, which spring strongly backward in nearly straight lines, bending somewhat suddenly to become continuous across the median ventral area. The growth lines indicate the presence of a deep hyponomic sinus, on either side of which project long points whose position is indicated by the two revolving sulci. In old age the transverse or radiating plications near the umbilicus die out, leaving the surface marked only by growth lines and the two revolving sulci. Periodic constrictions appear to be wanting.

The siphonal saddle is low and indented above. The remaining lobes and saddles two of each, are all rounded. The first lateral saddle projects far above the siphonal one and is narrower and somewhat higher than the second lateral. The pair of siphonal lobes are small, much smaller than the pair of laterals, which are as large as the lateral saddles.

In its young stages this form has a thick-discoidal shape, with volutions which are transverse, elliptical, flattened along the venter, and wrapped one upon the other, scarcely embracing at all. The umbilicus is practically the entire diameter of the shell. The height of the volutions increases more rapidly than the width, and at the same time they become more and more embracing, until the cross section is radially elongated and until the umbilicus occupies a fourth or less of the entire diameter. The characteristic sculpture is developed early, consisting at first of elongated nodes along the sides of the ventrally-flattened volutions. The two revolving sulci do not appear until later. By the gradual change in shape of the volutions and the gradual introduction and modification of the sculpture, the lateral plications appearing before the sulci and being lost before them in the gerontic stages, the characteristic features of this shell are evolved.

In its larval stage this form resembles Gastrioceras richardsonianum and occurs associated with it. It may be distinguished by being thicker, not compressed-discoidal, and by being marked by transverse costæ, coarser and stronger than the lire of the Gastrioceras.

Horizon and locality.-Caney shale, Tuskahoma quadrangle (station 2057), Antlers quadrangle (stations 2075, 3948), Atoka quadrangle (station 2082), McAlester quadrangle (station 2079), Tishomingo quadrangle (stations 2084, 2091, 5113).

Genus TRIZONOCERAS n. gen.

This type is represented by two species having very well-marked characters, which forbid uniting them with any of the genera known

to me.

The shape is more or less discoidal, with nearly closed umbilicus. The cross section is subtriangular to sublunate, narrow across the venter and expanded below in the typical species, and extending out near the umbilicus in auriculate projections. The surface appears to be smooth. The suture in its general scheme is like that of Paralegoceras, rather than Goniatites, there being three lobes and three saddles, besides a siphonal saddle, in the external suture. The siphonal saddle is narrow and indented above. The others are all rounded, the outer differentiated from the two inner ones by being larger and asymmetric. The outer lobe is correspondingly differentiated from the two inner lobes by being larger and simple and lanceolate, while the two inner ones are smaller and markedly bifid.

The apparent formation, upon each side, of a continuous revolving partition made by the outer sides of the second lateral saddles (see fig. 12 of Pl. XI) conspicuously divides the external portion of the volution into three parts, correspondingly occupied by the small median lobes and saddles, and the large, somewhat differently shaped lateral ones.

This genus is related to Dimorphoceras, but is clearly distinguished by important differences in the suture line.

Type.-Trizonoceras typicale.

TRIZONOCERAS TYPICALE n. sp.

Plate XI, figures 12, 12a. 12b.

This species is based upon a single mature specimen, which shows the following characters. The size is small, the general shape discoidal, with closed or nearly closed umbilicus. The volutions increase rapidly, so that the aperture occupies considerably more than half of the entire diameter. The cross section is subtriangular, very narrow across the venter, expanding below, and more or less projecting at the umbilicus in little ears.

The surface appears to have been smooth.

The siphonal saddle is rather narrow and high. It is deeply indented above, but this part of the specimen is obscure, and it can not be determined whether the indentation is angular, whether it is formed by two parallel lines which do not meet across the bottom, or whether the center is elevated into a denticle, thus making the saddle three-pronged. The first lateral lobe is considerably broader than the siphonal saddle, and is bifid or bilobed, by reason of a moderately strong, median, saddle-like depression at its end. The first lateral saddle is broadly rounded, about the size of the first lobe, and about the width of the siphonal saddle, though not so high. The second lateral lobe is somewhat smaller than the first, but, like it, bifid. The second lateral saddle, though similar to the first, is considerably larger. The third lateral lobe is larger than any of the others, and unlike them is simple and lanceolate. The third lateral saddle is much larger than the others; it is rounded, but instead of being regular is asymmetric. The internal sutures are not known.

The mesial portion of the structure of this species is rather sharply defined from the two lateral areas, having lobes and saddles which are not only smaller but differently shaped. There is another still more obvious peculiarity, which appears to divide the external portion of the shell into three distinct areas. The sutures occur very close together, and the external limb of the second lateral saddle not only almost connects with the same portion of the sutures preceding and following it, but, having the same direction, forms part of an apparently straight, continuous, revolving line. One of these occurs, of course, upon each side, and they appear to divide the sutural pattern into three quite distinct areas.

Horizon and locality.-Caney shale, Antlers quadrangle (station 3948).

TRIZONOCERAS LEPIDUM n. sp.

Plate XI, figures 13-14a.

This species can best be described by comparing it with the typical and only other known representative of the genus. The size is small and the rate of expansion rather rapid. The umbilicus is closed. The whorl section is sublunate, projecting at the umbilicus, and contracting, though rather broadly rounded above. It is thicker than T. typicale and more broadly rounded across the ventral surface. Consequently the shell as a whole is rather more globose. The suture is also different in detail, the outer zones being relatively narrower and the median one and the individual lobes which are comprised in it relatively wider. The surface is smooth, so far as known. Horizon and locality.-Caney shale, Atoka quadrangle (station 2082), McAlester quadrangle (stations 2078, 2079), Antlers quadrangle (station 3894), Tishomingo quadrangle (station 2091).

OSTRACODA.

Genus CYTHERELLA Jones.

CYTHERELLA aff. BENNIEI Jones, Kirkby, and Brady.

Plate V, figure 8.

The only station at which Ostracoda have been noted in the fauna under consideration is 3981. The material from this point is none too well preserved, but two widely different forms appear to be present in it. One of these has a deep transverse furrow, a spine, and a tubercle. The other seems to be without such distinguishing marks altogether. It is of about the same size as Entomis unicornis, with which it is associated. The shape is elliptical, a little less than twice as wide as long, somewhat contracting in front, and more or less rectilinear along the upper and lower margins. The convexity is moderate, rather abruptly rounding down at the margins, thickest behind. Surface smooth.

So far as can be determined from the material examined, the Caney form is closely related to the English one cited above."

Horizon and locality.-Caney shale, Ardmore quadrangle (station 3981).

Genus ENTOMIS Jones.

ENTOMIS UNICORNIS n. sp.

Plate V. figure 7.

Shell fabiform, about twice as wide as high or a little less. Hinge straight, somewhat shorter than the greatest width. Lower margin gently convex. Ends strongly and rather regularly rounded. A well-defined furrow perpendicular to the hinge begins a little in front of the middle and passes about halfway to the lower margin. Anterior portion of shell perhaps a trifle more convex than the posterior. A small but strongly elevated tubercle is situated close to the hinge and posterior to the front margin by about one-third the distance between the latter and the nuchal furrow. A short, stout spine projects backward from the posterior half. Its position is almost marginal, a short distance below and posterior to the end of the hinge line. Surface nearly or quite smooth, without the ridges which characterize the more common group of the genus.

The majority of the species of Entomis are marked by concentric or transverse ridges or liræ of greater or less fineness, though smooth species are not unknown. The present form is distinguished by its smooth surface and by the small spine projecting from near the posterior margin.

Horizon and locality.-Caney shale, Ardmore quadrangle (station 3981).

a Jones, T. R., Kirkby, J. W., and Brady, G. S., British Carboniferous Entomostraca; Palæontographical Soc., 1874-1884, p. 70.