194 
PALAEONTOLOGY OF NEW-YORK. 
tion and bifurcation, and are crossed by fine concentric striae. Interior 
indistinctly granulose. 
The original specimen from which Mr. Vanuxem described this species is the 
dorsal valve figured on Plate xxi, fig. 8 a. The shell is partially exfoliated, and the 
interior surface shows the fine concentric lines crossing the radiating strise. Fig. 1 a 
is a similar specimen proportionally shorter, being almost semicircular in form. I 
have referred to the same species the figures 3 b, c, d and e, Plate xvm, which are 
casts preserving the remains of the striee in a good degree of perfection. 
The great similarity in the surface markings, and the approximation in form of 
this species with S. woolworthana , suggest a doubt as to the propriety of separating 
the two as distinct species. 
The name Strophomena costellata of Conrad, in his catalogues in annual reports, 
was applied to this species. 
PLATE XXI. 
Fig. 8 a. A figure of the original specimen with the shell in part exfoliated. 
Fig. 8 b. Enlargement of the radiating and concentric striae. 
Fig. 9 a. A smaller individual from the same locality. 
Fig. 9 b. Enlargement of surface when the shell is partially exfoliated. 
PLATE XVIII. 
Fig. 3 b, c, d, e. Casts of the same species. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Columbia, Herkimer County; Hudson, etc. 
Strophomena conradi. 
Plate XYI. Fig. 13 & 14. 
Shell semielliptical, varying from length and breadth equal, to breadth 
one-fourth greater than the length. Hinge line scarcely equalling the 
greatest width of the shell. Dorsal valve very convex, and somewhat 
gibbous in the middle, regularly sloping on all sides, and scarcely flat¬ 
tened at the hinge extremities. Area unknown. 
Surface uniformly striated with fine sharp striae, which are rounded by 
exfoliation. 
This species is described from two individuals which present some variety of 
proportions, but which are essentially different from any other species known to me 
