138 
PALAEONTOLOGY OF NEW-YORK. 
In the Tully limestone of N$w-York, we have a Chonetes which I am unable 
to distinguish by any positive specific characters from the C. logani of Burlington 
and other western localities.. 
The shell is moderately concavo-convex, semielleptical, the length 
and breadth being about as 6 or 7 to 9 ; the cardinal angles scarcely 
extended beyond the width of the shell. The ventral valve is moderately 
convex, sometimes gibbous a little above the middle, with the umbo 
prominent, regularly curving to the front and abruptly depressed towards 
the cardinal angles. The dorsal valve is regularly and moderately con¬ 
cave in the middle and lower part, and flattened towards the cardinal 
extremities. 
The surface is marked by from twenty to forty low rounded costae, 
many of which are dichotomous towards the margin. These costae some¬ 
times become obsolete towards the cardinal angles, but are often distinct 
nearly to the hinge-line. The entire surface is marked by elevated undu¬ 
lating concentric striae which are sometimes equal to the space between 
them; but, when partially exfoliated (and sometimes in other condi¬ 
tions), are narrower than the intermediate spaces. 
The margin of the cardinal area preserve four (or six ?) somewhat 
strong oblique spines; the area is harrow. The interior of the dorsal 
valve is papillose, with a short cardinal process. Casts of the ventral 
Valve are very convex in the upper part, with a narrow slit marking the 
place of the median septum, and, below this, preserving the marks of the 
bifurcating striae, and sometimes the concentric striae are visible near 
the margin. 
In the shaly and calcareous rocks of Medina county, Ohio, there is a 
similar form of Chonetes, undistinguishable by any external characters 
from the specimens from the Tully limestone, except that the cardinal 
angles are sometimes a little more produced than is usual in that rock. In 
one specimen, equal in size to the largest from the Tully limestone, there 
are about forty costae on the margin, and these are crossed by elevated 
striae of precisely the same character. In numerous casts of the ventral 
valve, in the same association, there are characters similar to those 
noted in the Tully limestone specimens; the central or upper convex 
