402 PALAEONTOLOGY OF NEW YORK. 



conditions of T. obliquatum. T. distortum, Barrande, from the. Silurian strata of 

 Bohemia, is an allied form, but differs specifically in its greater curvature, 

 elliptical, transverse section, and shallower air-chambers. 



Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 



Trochoceras expansum, n. sp. 



I'l.ATES LVIII, FIG. 6; CXI, FKJ. R. 



' Troctutceras obliqualits. Hall (in part). Illustrations of Devonian Fossils: Cephalopoda, plate 48, 



fitfg. 5. 6. 1876. 



Shell large, nautiloid, gibbous, making about half of one volution, departing 

 • but little from one plane. The portion of a volution is curved in a sinistral 

 direction. Transverse section elliptical ; ventro-dorsal diameter about two- 

 thirds of the lateral. Tube regularly and rapidly enlarging. Apical angle 

 about 25°, but showing considerable variation, from the compressed nature 

 of the specimens. 



Chamber of habitation large, having a length less than the greatest lateral 

 diameter. Aperture not observed. 



Air-chambers regular, numerous, very gradually increasing in depth 

 toward the grand chamber, varying from 1.5 to 4 mm. in different indi- 

 viduals. Septa smooth, moderately concave, the concavity amounting to 

 about the depth of one air-chamber. The sutures curve toward the apex, 

 over the dorsal and ventral sides, and toward the aperture on the lateral faces 

 of the tube. Siphuncle small, close to the convex ventral side. 



Test and surface-markings unknown. Internal mould smooth, with the 

 sutures impressed. 



A small individual, retaining a portion of the chamber of habitation, with 

 six attached air-chambers, has a length of thirty-five mm., measured on the 

 lateral face of the tube. About eighteen mm. of this length pertain to the 

 grand chamber, which is somewhat compressed, and has a lateral diameter at 

 the base of thirty mm. One fragment shows fifteen air-chambers in the 

 length of forty mm., measured on the concavo-dorsal side. 



This species is distinguished from T. obliquatum by its nautiloid form, lesser 



