282 
PALAEONTOLOGY OF NEW YORK. 
Test strong, having a thickness of from one to two mm. on the chamber 
of habitation. Surface marked by very fine, minutely undulating irregular, 
lamellose lines of growth, crossed by indistinct, longitudinal striae. The 
ventral side is indicated by a broad sinus in the aperture and surface- 
markings, and a carina on the cast of the interior. 
The internal mould of the chamber of habitation is made characteristic by 
the constrictions of the tube, and the abrupt contraction of'the aperture. 
These features of the interior are less conspicuous on the exterior of the shell. 
An individual, consisting of the chamber of habitation entire, and about 
thirteen attached air-chambers, has a length of 115 mm., with a diameter 
near the aperture of over forty mm. 
This species is distinguished from 0. Marcdlense by its more gradually enlarg¬ 
ing tube, its much shorter and more characteristic chamber of habitation, the 
position and size of the siphuncle, the depth of the chambers, and the ornamen¬ 
tation of the test. It was formerly not distinguished from 0. Marcdlense; but 
an examination of all the characters has shown the very unlike features pos¬ 
sessed by this species. The want of sufficient material precludes any compari¬ 
sons based on the organic deposit, which is probably present in this species, 
as indicated by the ventral carina on the internal mould of the air-chambers. 
Formation and locality. In the Goniatite limestone of the Marcellus shale at 
Schoharie, N. Y. 
Orthoceras aptum, n. sp. 
PLATE XXXVIII, FIG. 8. 
Orthoceras typum (Saemann), Hai.l (in part). Illustrations of Devonian Fossils: Cephalopoda Explanation 
of pi. 38, fig. 8. 1S76. 
Shell straight, regularly and gradually enlarging from the apex to the aperture. 
Transverse section circular. Apical angle 5°. Initial extremity unknown. 
Chamber of habitation having a length of about three times the diameter at 
the last septum, expanding slightly beyond the general enlargement of the 
tube, with a very gentle constriction near the middle, which is shown on the 
cast of the interior. Chambers numerous, regularly increasing in depth 
