TREMATOSPIRA OF THE HAMILTON GROUP. 
S73 
The interior of the dorsal valve shows a strong deeply bilobed cardi¬ 
nal process, with the bases of slender crura ; the teeth sockets are large 
and deep ; there is a low median crest or septum, which is somewhat 
strong above, but dies out about the middle of the shell. In specimens 
which have been cut to show the spires, these appendages are slender, 
with about ten or eleven turns on each side. 
The proportions of length and breadth are about as three to four. 
The largest specimen observed is a little more than three-fourths of an 
inch in length, by an inch and one-sixteenth in width; while many of 
the specimens are less than half these dimensions. A well-formed speci¬ 
men of about three-fourths of an inch in length by one inch, has a depth 
of nine-sixteenths of an inhh. A very gibbous specimen measures three- 
eighths of an inch in length, nine-sixteenths in width, and half an inch 
in depth. 
The general aspect of this shell is similar to T. multistriata; but the form is 
usually less gibbous, the sinus more distinctly defined, and the striae are 
essentially simple. It is distinguished externally from Atrypa, by the granulose 
surface and punctate character of the shell. 
This fossil is not abundant, though not exceedingly rare. It is principally 
restricted to the western part of New-York, and has been found in Canada West. 
Trematospira hirsuta (Hamilton group). 
7 8 9 10 
Figs. 7 & 8. Dorsal and front views of a specimen. 
Figs. 9 & 10. Interior of the dorsal and ventral valves. 
Geological formation and localities. This species occurs on the shores of 
Canandaigua lake and at Bloomfield, Ontario county • at York and Moscow, Li¬ 
vingston county ; at Pavilion and Darien, Genesee county, and at Eighteen-mile 
creek in Erie county, New-York. In Canada West it occurs near Widder station 
on the Grand Trunk railway. 
I have received this species from Dr. James Kxapp, of Louisville, collected from 
the corniferous limestone at the Falls of the Ohio. 
The following figures in wood are illustrations of some of the typical species of 
Trematospira, from the Lower Helderberg group, described, and heretofore 
given in the State Cabinet Report. 
