CEPHALOPODA. 
399 
about equal in depth to the air-chambers. Sutures slightly oblique to the 
spiral axis. 
Siphuncle large, moniliform, expanding in the cavities of the air-chambers 
to nearly twice its diameter at the septa. The constrictions of the siphun- 
cular tube are marked by strong transverse strim. Its position on the ven¬ 
tral side is indicated on weathered specimens, where a portion of the tube is 
usually exposed. 
Test and surface-markings unknown. Near the aperture the cast pre¬ 
serves traces of strong lamellose lines of growth. Internal mould essentially 
smooth, showing the crenulations at the base of the grand chamber, and the 
suture lines but slightly impressed. 
One specimen, consisting of the chamber of habitation, and six attached 
air-chambers, has a length of ninety mm., of which about thirty mm. pertain 
to the chamber of habitation, which has a transverse diameter of sixty-five 
mm., measured near the aperture. A similar fragment, retaining eight air- 
chambers, has a length of 125 mm., measured on the convex side of the tube. 
This species is remarkable for its very gibbous, nautiloid form, large apical 
angle, and the depth of the air-chambers. It is more involute than any of the 
succeeding species, although resembling in its nautiloid character T. expansum, 
which is distinguished by a lesser curvature, shallow air-chambers, and form 
of transverse section. The forms without annulations, which have preceded, 
including T. eugenium and T. Orion, are conspicuously different in the contrac¬ 
tion of the tube toward the aperture, and its more gradual enlargement from 
the apex. The characters of the siphuncle are similar to many species of Gom- 
phoceras (see G. eximium ), and have not been observed in the other species of 
the genus described in this volume. 
Formation and localities. In the Schoharie grit, Schoharie and Albany 
counties, N. Y. 
