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ORTHOCERAS TETRICUM.

PLATES LXXVIII B, FIG. 4; LXXX, FIGS. 2, 5, 6, 8, 9.

Orthoceras tetricum, HALL (see O. pravum). Descriptions of New Species of Fossils, etc., p. 45. 1861. SHELL straight, regularly and very gradually enlarging from the apex. Transverse section circular. Apical angle varying from 4° to 510. Initial extremity unknown.

A small portion of the chamber of habitation has been observed, having a length of fifty mm. This fragment shows nothing more than a regular expansion conforming with the general contour of the tube. Air-chambers large, extremely irregular in depth, varying from twelve to twenty-two mm. Aperture unknown.

Septa thin, smooth, very concave. The concavity is equal to an arc of about 140°. Sutures straight, and horizontal.

Siphuncle excentric, situated a little less than one-third the diameter of the tube from the ventral (?) side. Its elements, in its passage through the chambers, have not been observed; at the septa the diameter is nearly four mm., where the entire tube has a diameter of thirty mm.

The test was probably very thin, as it has only been observed in two individuals. Its thickness, as imperfectly preserved, is not more than one mm. Surface marked by very fine, sharp, regular, gently-curving, concentric striæ, as shown in fig. 4 of pl. 78 B.

The internal mould shows the walls of the chambers to be smooth, and continuous with the regular enlargement of the tube.

No entire individuals have been observed. The longest fragment has a length of 130 mm., with a diameter at the larger end of forty mm., measuring twenty-eight mm. in diameter at the smaller extremity. The entire specimen was probably several times the length of this fragment. Several fragments of larger individuals have a diameter of about fifty mm.

This species is easily distinguished from O. procerus by its more gradually enlarging tube, and large, deep air-chambers; and also that none of the specimens

show an organic deposit. It is closely allied to O. collatum, and may be distinguished by its more distant septa and their greater concavity. The specimens do not preserve enough of the chamber of habitation to admit of comparisons with O. collatum in this particular.

Formation and localities. In the Schoharie grit at Schoharie, and in the Helderberg range.

ORTHOCERAS COLLATUM, n. sp.

PLATE LXXX, FIGS. 1, 3, 4.

SHELL straight, regularly and gradually enlarging from the apex to a point near the aperture. Transverse section subcircular, often much flattened from compression. Apical angle varying from 4° to 6° in the specimens. Initial point unknown.

Chamber of habitation large, slightly expanding beyond the general enlargement of the tube, to a point anterior to the middle, where it is abruptly constricted. In front of the constriction the tube expands gradually towards the aperture. Aperture not observed. Air-chambers regular, having a depth of about eleven mm.; walls flat and smooth. The ventral side is indicated by a low, longitudinal carina on the chamber walls, which is more prominent on the anterior portion. This line is shown on the casts of the interior, and has a width of about one mm.

Siphuncle large, slightly excentric, having a diameter at the septa of nearly four mm. Its elements in its passage through the chambers have not been observed.

The characters of the test and its ornamentation are not shown on any of the specimens at hand. It was probably thin and has been dissolved, leaving a cast of the interior.

The internal mould is essentially smooth. The ventral carina and the marked constriction of the chamber of habitation are the only distinctive features.

A fragment preserving eight air-chambers measures eighty-eight mm. in length, and has a diameter of forty-five mm. One specimen retaining the chamber of habitation and five ordinary chambers, has a length of 125 mm., with a diameter near the aperture of thirty-five mm.

This species closely resembles O. tetricum, but is readily distinguished by its more regular and frequent septa, their lesser concavity, and the decided constriction of the chamber of habitation,

Formation and localities. In the Schoharie grit at Schoharie, and in the Helderberg mountains.

ORTHOCERAS STYLUS.

PLATES XXXVI, FIGS. 2, 3; AND LXXIX, FIGS. 1, 3.

Orthoceras baculum, HALL. Descriptions of New Species of Fossils, etc., p. 46.

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1862.

Illustrations of Devonian Fossils: Cephalopoda. Explanation of plate 36 figs. 3, 4. 1876.

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baculus, BARRANDE. Syst. Sil. du centre de la Bohème, vol. 11, text 3, p. 118. 1874.
stylus, HALL. Catalogue of American Palæozoic Fossils (S. A. Miller), p. 245. 1877.

SHELL an extremely slender, straight, cylindro-conical tube. Transverse section circular. Apical angle 20. Apex unknown.

Chamber of habitation long, cylindrical, length more than six times the transverse diameter, showing no variation from the general contour of the tube. Aperture not observed. Air-chambers regular, shallow, the depth being about five mm. Usually the last two are shallower than the posterior chambers.

Septa thin, ornamented with a small, circular areola around the insertion of the siphuncle; concavity equal to an arc of from 115° to 120°. Sutures straight and horizontal.

Siphuncle small, subcentral or slightly excentric, diameter 1.5 mm. at the septa, where the diameter of the tube is fifteen mm. Its characters have not been observed in its passage through the chambers.

The test has not been preserved, but the surface characters are sometimes

retained by the casts of the interior, and show that it was marked by fine, curving, transverse striæ.

The internal mould is smooth, and the chamber walls essentially flat.

A specimen 130 mm. long, and preserving about ninety-five mm. of the chamber of habitation, is scarcely appreciably diminished towards the apex, the greatest actual diameter being in the middle of the length. Another fragment of ninety-five mm. in length, of which thirty-five mm. pertain to the chamber of habitation, shows scarcely a diminution in the diameter. The first of these specimens has a diameter of fifteen mm., and the second of twelve mm.

This species is remarkable for its slender, cylindrical form, resembling O. exile of the Hamilton group, but is distinguished by its smaller size, greater attenuation, and the absence of any constriction of the chamber of habitation. From O. tetricum it differs in its very small apical angle, the much greater frequency of the septa, and the central or slightly excentric siphuncle.

In its vertical distribution this species is confined to the Schoharie grit, but it is one of a small group of forms continuing through the Upper Helderberg limestones, and the Hamilton group.

Formation and localities. In the Schoharie grit at Schoharie, and the Helderberg range.

ORTHOCERAS MEDIUM, n. sp.

PLATE LXXIX, FIGS. 11, 12.

SHELL straight, gradually expanding. Transverse section circular. Apical angle about 50. Initial point unknown.

Chamber of habitation not observed. Air-chambers irregular in depth, increasing toward the grand chamber, varying from five to ten mm. in the length of forty mm. In the cast, the ventral side of the chamber walls is ornamented by a elongate-conical carina, extending from the anterior portion of each chamber about two-thirds of its length.

Septa thin, smooth. Sutures horizontal, straight.

Siphuncle slightly excentric, having a diameter at the septa of two mm. where the tube has a diameter of eleven mm. It has not been observed in its passage through the interseptal spaces.

The test has not been preserved. Surface characters unknown.

The internal mould is smooth with the exception of the ventral carina. The walls of the chambers sometimes become concave, and occasionally the concavity is shown as a flat, slightly depressed constriction or belt.

One small fragment has five chambers in the space of thirty-five mm., with a diameter at the larger end of twelve mm. A fragment of the septate portion of a larger individual has ten chambers in the space of sixty-five mm. This species is intermediate in its characters between O. stylus and O. pravum. It differs from O. stylus in its greater apical angle, generally deeper and more irregular chambers, and the prominent line on the ventrum. From O. pravum it is distinguished by the absence of any areolar markings and ornamentation on the septa.

Formation and locality. Observed only in the Schoharie grit at Schoharie, N. Y.

ORTHOCERAS PRAVUM, n. sp.

PLATES XXXV, FIG. 14; XXXVI, FIG. 1; LXXXI, FIGS. 1-8; AND CXII, FIGS. 15–17.

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Orthoceras tetricum, HALL. Descriptions of New Species of Fossils, etc., p. 45. 1861.
Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 73. 1862.
Illustrations of Devonian Fossils: Cephalopoda, pl. 36, fig. 2. 1876.

SHELL straight, regularly and gradually enlarging, usually very much distorted from compression. Transverse section circular, often flattened and unsymmetrical. Apical angle about 5o.

Only a small portion of the chamber of habitation has been observed. This fragment presents no unusual features. Air-chambers regular, deep, varying from eight to fourteen mm. in depth, in the same and in different individuals.

Septa regularly and deeply concave, the concavity being equal to an arc of 140°. Sutures straight and horizontal, often curved and oblique from distortion. Septa ornamented by a raised lamellose-striate areola around

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