I»4 PALEONTOLOGY 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 striae. Fig. ] a 

 is a similar si)ecimen proportionally shorter, being almost semicircular in form. I 

 have referred to the same species the figures 3 b, c, d and e, Plate xviii, which are 

 casts preserving the remains of the strise in a good degree of perfection. 



The great similarity in the surface markings, and the approximation in form of 

 this si>ecies with S. woolworthana, suggest a doubt as to the propriety of sepai-ating 

 the two as distinct species. 



The name Strophomena costeUata 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 Btrise. 

 Fig. 9 a. A smaller individual from the same locality. 

 Fig. 9 6. Enlargement of surface when the shell is partially exfoliated. 



PLATE XVIIL 

 Fig. 8 h, 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. 



Platk XVI. Fio. 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 diflFerent from any other species known to me 



