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Siphuncle central or subcentral, small, the diameter being about two mm. where the tube has a diameter of thirty-five mm. The character of the siphuncle in the interseptal spaces is unknown,

Cast of the interior essentially smooth. The ventral side is indicated by a longitudinal raised line or carina on the cast of the septate portion. Test and surface-markings unknown.

The incomplete individual, fig. 2, pl. 76, has a length of 220 mm., and a diameter, at the base of the chamber of habitation, of fifty-five mm.

The accompanying figures offer an explanation of the appearance, described above, as produced by weathering. Figure 1 is a portion of a longitudinal

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FIG. 1.

S
FIG. 2.

section of the tube of a perfect specimen, showing the epidermal layer, e, and the nacreous layer, n. Portions of the septa are represented, continuing from s to z.

C, C, are air-chambers filled with infiltrated matter, or material similar to the surrounding rock. Figure 2, a section of a weathered specimen, with the consequent removal of all exposed shelly matter. z, z, are the zones, or narrow, shallow furrows, as represented in figure 2, plate 76.

This form is distinguished from O. fluctum by the distance and rigid appearance of the septa, and their produced margins, and by the keel along the ventral side. It also resembles O. Tantalus, but the septa are not so frequent or oblique. Formation and locality. This species is known only from the Schoharie grit, in the vicinity of Schoharie, N. Y.

ORTHOCERAS TANTALUS, n. sp.

PLATES XXXV, FIGS. 8-10; XXXV A, FIGS. 7, 10.

SHELL large, straight, regularly expanding from the apex. Transverse section circular. Apical angle 9° to 10° 30'.

Chamber of habitation large; but its proportions are not fully determined, owing to the imperfection of the specimens. Aperture unknown. Air-chambers numerous, regularly increasing in depth to the chamber of

habitation, varying from five to eight mm. This species also presents, in a less marked degree, the zoned appearance of O. cingulum, caused by the removal of the shelly margins of the extended septa; otherwise the cast of the interior is smooth.

Septa having a concavity equal to an arc of about 110°. Plane of the septa straight, and slightly oblique; convex surface ornamented by an elevated areola around the siphuncular scar, and generally by an irregular, vesiculose, organic deposit around the siphuncle, which sometimes reaches a diameter of more than one-third that of the tube. Occasionally this deposit consists of irregular tubercles and flattened expansions, extending nearly to the septal margins. The character and appearance of this organic deposit on the septa and siphuncle varies greatly in the same individual, depending upon the distance from the chamber of habitation. Near the apex it assumes a more marked complexity of detail, often nearly filling the chambers, and obscuring the characters of the septa and siphuncle.

Siphuncle apparently straight, with the walls sometimes variously thick

ened on the exterior.

Test unknown. Casts of the interior marked by an elevated line along the septate portion, indicating the ventral side of the shell, and free from any other markings so far as observed.

This fossil is only known in a fragmentary condition. When entire, the tube probably had a length of one foot and a half, or about 450 mm.

From O. Ohioense this species is distinguished by the absence of any curvature of the tube, and by the organic deposit on the septa and siphuncle. It resembles O. Pelops in the character of the surface of the casts; but the septa are more closely arranged, and their concavity not so great. In the incomplete examinations made previously to the publication of the Illustrations of Devonian Fossils, this form had not been separated from O. Pelops, and in the crushed and imperfect condition of a large proportion of the specimens of this formation, the distinction between the two species is not always conspicuous. In the distance of the septa and comparative attenuation of the tube, this form differs little from well-preserved specimens of O. luxum; but the concavity of

the septa in the latter is greater, and the siphuncle is expanded between the septa. The organic deposit is very similar in the two species.

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

ORTHOCERAS OBLIQUUM, n. sp.

PLATE LXXVIII, FIGS. 1-4..

SHELL straight, robust, transverse section subcircular. Tube regularly and somewhat rapidly expanding from the apex. Apical angle from 9° to 10°. Initial extremity unknown.

Chamber of habitation very large, regularly expanding to the aperture. The cast of the interior is smooth. Aperture not observed. The air-chambers numerous and shallow, having a depth of from one-sixth to one-seventh of the diameter of the tube, or from three to five mm.

Septa thin, smooth, with a small areola around the insertion of the siphuncle. The suture line is curved on two of the sides, and very oblique over the other two sides. The arc of curvature of the septa, measured from specimen, fig. 3, is about 130°. The small specimen, fig. 4, apparently belongs to this species, but is much flattened, and the curvature of the septa destroyed.

Siphuncle subcentral, small, diameter at the septa equal to about onethird the depth of the chamber. The character of the siphuncle in its passage between the septa has not been observed; one longitudinal section indicates that it was probably expanded or moniliform.

The largest fragment has a length of 220 mm., and a diameter of fifty mm., at a point near the aperture. None of the specimens referred to this species preserve any evidence indicating the thickness and ornamentation of the test,―all being in the condition of casts of the interior.

This species somewhat resembles O. fluctum, but is distinguished by its more rapidly enlarging tube, the greater obliquity and lesser curvature of the septa; which are also more convex than in that species. In its vertical

distribution, so far as known, this species is confined to the upper beds of the

Schoharie grit.

Formation and locality. Schoharie grit, Schoharie, N. Y.

ORTHOCERAS LUXUM.

PLATES XXXV, FIGS. 4-7; LXXVI, FIG. 1; LXXVII, FIGS. 1-8; LXXVIII, FIGS. 5-7; LXXVIII B, FIG. 3; LXXXI, FIG. 13; CXII, FIGS. 12-14.

Orthoceras luxum, HALL. Illustrations of Devonian Fossils: Cephalopoda, pl. 35, fig. 5. 1876. SHELL straight, regularly and gradually enlarging from the apex. Transverse section, in the better preserved individuals, circular. Apical angle varying, owing to the compressed condition of the specimens, from 9° to 11°. Apex unknown.

The chamber of habitation is rarely preserved, and has no unusual characters. So far as observed, it regularly enlarges to the aperture without any constriction or contraction. Aperture unknown. The air-chambers are regular, gradually increasing in depth from the apex to the grand chamber. The depth of the interseptal spaces varies from six to three mm. in the same and in different individuals. In specimens retaining their normal form, the outer walls are flat, not deviating from the general attenuation of the tube. In compressed forms, the walls are conspicuously concave.

Septa thin, regularly concave; the concavity equal to an arc of about 113°. Many of the specimens vary from this amount of concavity according to the various degrees of compression and distortion to which they have been subjected. The convex side of the septum is marked by a distinct. areola surrounding the siphuncle, and extending in a kind of vascular expansion unequally, and on one side, often reaching to the margins of the septum, and affecting the ventral portion of the cavity. This areolar marking is often thickened, becoming striated at the margin, and spreading over the septum as a mammillary organic deposit.

Siphuncle central, moniliform, greatest diameter between the septa equal to nearly three times the diameter in its passage through the septa, or equal

to the depth of the chambers. Specimens in which the siphuncle has become exposed by weathering, show that it was obscurely lobed and longitudinally ribbed.

The test was probably thin. No portions of it are preserved in any of the specimens observed. The surface, as shown by the internal casts of several individuals, was marked by lamellose, transverse striæ.

The appearances of the internal mould of this species are very characteristic. The exsolute, or lax condition of the chambers, together with their concave margins — a uniform condition of the compressed specimens is a distinguishing feature. The organic deposit is shown in all casts of the interior, and is peculiar to the species.

The largest fragment referred to this species has a length of 200 mm. Other fragments have been found belonging to larger individuals. The maximum length was probably not more than 400 mm.

The organic deposit on the septa, around the siphuncle, and on the ventral walls of the air-chambers, presents many different aspects, and has been observed in numerous individuals. It increases in amount and complexity of detail, from the chamber of habitation to the apex. In some specimens the siphuncle has been absorbed or obliterated by the deposit. Other specimens show a deposit formed on the interior of the siphuncular tube. The filling up of the chambers is not, however, carried to such a remarkable extent as in O. oppletum, but is much more marked than in any of the preceding species. The deposit on the septa varies in different portions of the tube, and on different sides. Sometimes the amount is very marked on one side (see fig. 3, pl. 78 B), and less prominent or nearly absent on the other. The appearance produced is generally a pitting or erosion of the material filling the chambers. In well-preserved specimens, it is shown that these pits are the casts of the original deposit, which consists of closely arranged, irregular, mammillary aggregations of calcareous matter. The globules composing these masses are usually very small, occasionally reaching a diameter of two mm. The appearance around the siphuncle is, at first, that of a simple areola; the amount of deposit increasing till it becomes thickened, and

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