CEPHALOPODA. 399 



about equal in depth to the air-chambers. Sutures slightly oblique to the 

 spiral axis. 



Siphuncle large, moniliforra, 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 striae. 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, w,hich 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. eugemum 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. 



