CEPHALOPODA. 
393 
Siphuncle small, subcentral, having a diameter of one mm. where the tube 
has a ventro-dorsal diameter of thirteen mm. A small areolar depression 
on the convex side of the septa indicates a moniliform expansion of the 
siphon in the cavities of the air-chambers. 
Test thin, not well preserved. Surface subreticulate, marked by fine, 
regular lines of growth, crossed by regular, sharp, more distant, longitudinal 
striae, of which there are six to nine in the space of four mm. on the outer 
volution. Tube ornamented with regular, curved, oblique annulations, 
crossing the septa, and of about twice their frequency. On the internal 
mould the annulations are more rounded than on the exterior of the test, 
and are not continued over the concave dorsal side, being most prominent 
along the ventrum; becoming more distant and less marked on the chamber 
of habitation in large individuals. The sinus is indicated by a slight retral 
bend in the annulations and surface striae on the convexo-ventral side. 
The internal mould shows the annulations subdued, with some traces of 
the surface-markings. Sutures but slightly impressed. 
One specimen, measuring thirty-five mm. across the volutions, has a 
diameter, near the aperture, of sixteen mm., and an elevation of the helix of 
about twenty mm. The largest specimen observed has a diameter, across 
the disc, of nearly eighty-five mm. 
This species is distinguished from T. discoideum by its more gradually enlarging 
tube, smaller umbilicus, more elevated spire, and shallower air-cliambers ; the 
annulations are more frequent, and have less the character of transverse 
nodes, than in that species. It somewhat resembles T. Hwrnesi , Bare., from the 
Silurian system of Bohemia, in its surface characters and form of the tube; 
but the position of the siphuncle is different, and in that species the helix is 
dextral. 
This is the most abundant form of this genus in the Schoharie grit, but the 
specimens are mostly fragmentary, and in a very imperfect condition of 
preservation. 
Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 
50 
