septum, and its walls are apparently nearly uniform and straight in its passage through the air-chambers.

The test, inferring from the crystalline matter remaining on some parts of the surface, has had a thickness of about two mm. Surface marked by irregular, lamellose striæ. Internal cast smooth, with the exception of the constriction of the outer chamber, before noticed, and without special elevation or depression of the interseptal spaces.

This species differs from O. Pelops, which it closely resembles, in the more gradual expansion of the tube towards the aperture, and in the greater proportional distance of the septa, which are about as five to seven, and also in their greater concavity. In the gradual expansion of the tube, and distance of the septa, it approaches some of the forms in the higher rocks, from which it is otherwise very distinct. See O. Eriense, plate 40, of the Hamilton group, and O. Atreus, of the Portage group.

Formation and locality. This species occurs in the upper beds of the Schoharie grit, near Clarksville, Albany county, N. Y.

ORTHOCERAS OHIOENSE.

PLATES XXXV A, FIGS. 8, 9; XXXVI, FIG. 4.

Orthoceras Pelops, var. Ohioense, HALL. Illustrations of Devonian Fossils: Cephalopoda, pl. 36, fig. 1. 1876 SHELL slightly curved-curvature exogastric. Transverse section circular. Cone regularly and gradually enlarging. Apical angle about 9°. Initial extremity unknown.

Chamber of habitation large, the portion preserved in an imperfect specimen being about twice as long as its diameter at the base. Aperture unknown, apparently slightly contracted.

Septa thin, obliquely curved with regard to the axis of the shell, the margins being advanced further forward on the concave or dorsal side of the shell; in the smaller part of the shell (in the specimen figured), distant about one-sixth, and in the larger portion, near the outer chamber, about oneseventh of the diameter, varying in actual measurement from five to seven

mm., the last air-chamber being shallower than any of the preceding. The depth of curvature of the arc measuring the concavity of the septa is about one-fourth the diameter of the tube at the same point; and the arc of the circle subtends an angle of about 95°.

Siphuncle slightly excentric, being nearer to the convexo-ventral side of the shell, small at its passage through the septa; but a longitudinal section has given no satisfactory evidence of its character, or of its existence in the interseptal spaces.

Test entirely unknown, and no evidence of ornamentation visible upon the cast of the interior. Internal cast of the outer chamber apparently smooth, the septate portion showing a moderate convexity of the filling of each airchamber, which may, however, be in part due to the mode of weathering.

The specimen figured, and the only one positively identified, has a length of about 240 mm., with a diameter at the larger extremity of fifty-eight mm., and at the smaller extremity of thirty-five mm. The chamber of habitation measures 100 mm., and the septate portion, on the exterior, measures 130 mm., and embraces twenty air-chambers.

This species, from cursory examination, was originally noticed as a variety of O. Pelops, the slight curvature being regarded as accidental. A study of the specimen proves it to be a very distinct species. The curvature is apparently normal, and the extension of the septa on the concave side offers farther evidence of this fact. In the dimensions of the siphuncle at the septa, and the distance and curvature of the septa, it resembles the O. Tantalus, as shown in pl. 35, figs. 8-10, and pl. 35 A, fig. 7. In its external characters it might not readily be distinguished from that species, but the curvature and obliquity of the septa, and the excentricity of the siphuncle, are characteristic features. Besides, it has not the peculiar organic deposit on the septa and siphuncle possessed by O. Tantalus.

Formation and locality. This species is known to me only in the limestone of the Upper Helderberg formation, at Delaware, Ohio.

ORTHOCERAS MASCULUM, n. sp.

PLATE LXXVIII B, FIG. 1.

SHELL large, straight. Transverse section circular. expanding. Initial extremity unknown.

Tube very gradually

Chamber of habitation not observed. Depth of air-chambers varying from ten to sixty-five mm.; their internal casts, in the specimen figured, show a crenulated or tuberculated band at the anterior portion of each.

Septa irregular, generally very distant, straight and horizontal; concavity

unknown.

Position of the siphuncle not determined. Test removed from all observed specimens.

The internal mould is essentially smooth, with the exception of the crenulated bands above mentioned. The chamber walls are flat, with the septal sutures but slightly impressed. The specimens are often covered with numerous individuals of a species of SPIRORBIS.

One fragment having a diameter of eighty mm., and containing four air-chambers, measures 200 mm. in length. A similar specimen, with a diameter of nearly 100 mm. and seven air-chambers, has a length of 220

A smaller fragment with a diameter of the tube of sixty mm., and possessing nearly four air-chambers, has a length of 180 mm. Several large sections, referred to this species on account of their size, have a diameter of from 105 to 125 mm.

This species is remarkable for the large size and very gradual enlargement of the tube, and the extreme variation in the depth of the chambers. These characters distinguish this form from any associated species, or any species now known in the Devonian period.

Formation and localities. From the Schoharie grit, in the vicinity of Schoharie, and near Clarksville, Albany county, N. Y.

ORTHOCERAS FLUCTUм, n. sp.

PLATE LXXVI, FIGS. 4-7.

SHELL straight, gradually enlarging from the apex to the outer chamber. Transverse section subcircular, or broadly elliptical. Apical angle 8°. Initial point unknown.

Chamber of habitation large and regularly expanding towards the aperture, without any constriction so far as observed. Aperture unknown. Airchambers numerous and comparatively shallow, having a depth of four or five mm. when the diameter of the tube is thirty to thirty-five mm., but often showing variation of depth in adjacent chambers.

Septa thin, the concavity greater than the interspaces, being about seven mm., or equal to an arc of 100° to 108°. Sutures much curved, but not oblique to the axis.

Siphuncle central or subcentral in well-preserved specimens, and small at its insertion in the septa, participating in the effects of pressure, as shown in fig. 7. Its passage through the interseptal spaces has not been traced; but in some specimens the convex sides of the septa present an elevated areola, with vascular markings surrounding the siphuncular scar.

There is rarely any evidence of test preserved, it having been dissolved and removed; and the surface-markings are unknown. The internal casts are essentially smooth, the interseptal spaces being flat, with an intermediate groove made by the solution of the calcareous matter at the margins of the septa. The greatest length of the fragmentary specimens is about 200 mm.; but the length of entire individuals has probably been twice as great. The diameter of the tube at the last septum, in a well-preserved specimen, is thirty-five mm.

This species in many respects resembles the O. procerus; but it is less attenuate and proportionally less expanded in the outer chamber. The position of the siphuncle is also distinctive, while the septa, which are of the same frequency in both species, are in this one curved upon their exterior

margins, and the curvature unsymmetrical. All the specimens referred to this species agree in this feature of the septa. Figure 3, of the same plate, resembles this species, except in the greater distance between the septa. The view of the specimen represented is the much flattened and weathered dorsal side. The ventral side of the specimen is less compressed, and shows the septa to be straight and horizontal; the air-chambers are grooved and ornamented by a longitudinal carina, as partially represented in figure 2 of O. cingulum. In some of its phases this species resembles O. luxum; but the septa are more closely arranged, and the position and character of the siphuncle is quite different. In its vertical distribution this species is not known beyond the limits of the Schoharie grit, and its geographical distribution is confined, so far as at present known, within the counties of Albany and Schoharie.

Formation and localities. In the Schoharie grit in Schoharie, and at the base of the Helderberg mountains, N. Y.

ORTHOCERAS CINGULUM, n. sp.

PLATE LXXVI, FIGS. 2, 3.

SHELL straight, regularly and gradually enlarging. Transverse section, judging from the degree of compression, subcircular. Apical angle varying in compressed specimens from 6° to 80. Initial extremity unknown.

Chamber of habitation having only a small portion of the base preserved in the specimens examined; the internal cast of this portion is smooth, and very gradually enlarging. Air chambers numerous, regularly increasing in depth from the apex of the specimen to the chamber of habitation, varying in depth from five to ten mm. in the space of 140 mm. Internal cast of the walls essentially smooth, except at the base of each chamber in weathered specimens, where the produced septal margins are dissolved, giving the specimens a peculiar banded or zoned appearance.

Septa horizontal and straight on the margins, presenting a rigid appearance in specimens not disturbed by compression; marked by a raised areola around the insertion of the siphuncle, which is surrounded by vascular markings.