ire PALiEONTOLOGY OF NEW-YORK. 



This species has a general resemblance to 0. oblata, but is more nearly circular, 

 and sometimes longer than wide. The ventral valve is conspicuously sinuate in the 

 middle, and curves downwards to the margin, instead of spreading laterally with a 

 general concave surface. The area is larger and proportionally higher. 



Fig. 1 a, b, c, d. Ventral, dorsal, profile, and front views of a small specimen. 

 Fig. 1 e. Cast of the ventral valve of a larger individual, showing the vascular and muscular 

 impressions. 



Geological position and locality. In the Upper Pentamerus limestone of the Lower 

 Helderberg group : Helderberg mountains; Schoharie. 



Orthis multistriata (n. s.). 



Plate XV. Fio. 2 a - t. 



Shell circular or transversely suboval. Ventral valve most convex near 

 the beak, depressed below so as to form a broad shallow undefined 

 sinus, which sometimes gives to the front a subemarginate aspect : 

 beak more prominent than the opposite, slightly incurved. Dorsal valve 

 more elevated, gibbous between the middle and the beak : beak rising 

 above the hinge, obtuse and incurved. Hinge line straight, about half 

 the width of the shell. Area small, high. Foramen narrow, extending 

 nearly to the apex. 



Surface marked by fine, crowded, nearly equal striae, which increase 

 chiefly by implantation, and are crossed by a few faint concentric lines 

 of growth. 



Casts of the interior of the dorsal valve show very strong bilobed muscular im- 

 pressions, which are broad and strongly striated below, and narrowed above. From 

 the base of the muscular imprints radiate strong vascular impressions, which, in 

 numerous finer ramifications, reach the base of the shell. 



The cast of the ventral valve shows a deeply lobed subtriangular imprint of the 

 muscular impressions, with rarely some remains of the vascular impressions ex- 

 tending downward into the broad sinus, which is even more strongly marked in 

 the cast than in the shell itself. 



This species is closely related to Orthis tulliensis of the Hamilton group, and is 

 also a representative of the European Devonian and Carboniferous 0. resupinaia, 

 particularly the more ventricose varieties of that species. So many distinct species, 



