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. 
PLATES LVIII, FIG. 6; CXI, FIG. 5. 
Trochoceras ohliquatas. Hall (in part). Illustrations of Devonian Fossils: Cephalopoda, plate 48, 
figs. 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 
