176 
PALAEONTOLOGY OF NEW-YORK. 
This species has a general resemblance to O. 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 positio?i and locality. In the Upper Pentamerus limestone of the Lower 
Helderberg group : Helderberg mountains; Schoharie. 
Ortliis multistriata (n. s ). 
Plate XV. Fig. 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 Ortliis tulliensis of the Hamilton group, and is 
also a representative of the European Devonian and Carboniferous 0. resupinata , 
particularly the more ventricose varieties of that species. So many distinct species, 
