CHAZY LIMESTONE. 19 
SHELLS, TRILOBITES, &c. OF THE CHAZY LIMESTONE. 
Prats IV. (bis). 
28. 1. LEPTASNA PLICIFERA (n. sp.). 
Pu. IV. (bis). Figs. 1 a, 0. 
Semi-elliptical, much wider than long ; convex valve slightly depressed along the centre, 
from beak to base; surface marked by about 34 or 36 equal, somewhat coarse striae, which 
radiate, apparently in pairs, from the apex of the shell, intermediate ones often appearing 
towards the margin ; strie sharp, with rounded grooves between ; visceral cavity, as shown 
by the cast, duplicate, separated by a sharp ridge, which extends towards the base of the 
shell. 
Width + to # of an inch; length #3 to 4 of an inch. 
The condition of nearly all the shells of this species, which I have seen, is such as to 
render clear and definite descriptions almost impossible. It is mostly preserved in impres- 
sions of the outer shell, or as casts. It is quite unlike any species in the Trenton limestone, 
but approaches in some degree a small one in the Hudson-river shales. 
Fig. 1 a. Figure of the convex valve. 
Fig. 1 8. Cast of convex valve, with a portion of the shell remaining : cast of visceral cavities magnified. 
Position and locality. This occurs in great numbers in some thin layers of limestone near 
the higher part of the mass, at Chazy, Clinton county. 
29. 2. LEPTANA INCRASSATA (nm. sp.). 
Pu. IV. (bis). Figs. 2 a, 0, ¢. 
Shell thickened, almost semicircular ; dorsal valve very convex near the beak, gradually 
becoming flattened on the disc, and suddenly bending upwards near the margin ; ventral 
valve moderately concave, exhibiting a thickening near the margin; surface marked by 
sharp elevated radiating lines, between which are broader spaces. 
The surface of this species presents a kind of thickening which partially obliterates the 
strie ; the ventral valve particularly exhibits this sort of incrassation. It occurs with the 
last described in considerable numbers, but differs in being larger, thicker and more convex, 
as well as in the form of the visceral markings. This species often bears some resemblance 
to L. interstrialis of the Trenton limestone, but is a much smaller shell, and differs from 
the young of that species in essential points. 
Fig. 2 a, b, Convex valves of this species. 
Fig. 2c. Ventral valve. 
Fig. 2 d. Cast of the interior of the convex valve, and the same enlarged. 
Position and locality. In the thinbedded limestone, upper part of the mass, Chazy, 
Clinton county. (State Collection.) 
3* 
