60 



PALiEONTOLOGT OF NEW-YORE. 



This is a very beautiful species, found in the upper green shale at Rochester, more com- 

 monly than elsewhere. The stria; are usually unequal in size, increasing not by regular bi- 

 furcation, but by the appearance of a small one between the larger, which, if followed, becomes 

 in turn large, while a smaller one takes rise between it and the next : in some instances, the 

 increase is by regular bifurcation. The fine concentric striae are often obsolete. The shell is usual- 

 ly marked by several oblique plications along the hinge-line on each side of the beak, but these 

 marks are not always visible in compressed specimens. In these oblique folds the shell resembles 

 a species of the Trenton limestone (L. subtenta), but it is entirely distinct. The interior of the 

 dorsal valve is striated nearly to the beak, and the striss appear to be regularly bifurcating. 



Fig. 2 a. A young individual, with the strias very unequal, and the folds on the hinge-line scarce- 

 ly conspicuous. 



Fig. 2 b. A larger individual, with the shell partially removed from near the beak. 



Fig. 2 c. The interior of a dorsal valve, showing the striae equally bifurcating. 



Fig. 2 d. An old individual, with the shell entirely removed about the beak, and partially re- 

 moved from other portions ; the concentric striae being still partially preserved. 



Fig. 2 e. An obscure cast in sandstone, where the striae appear to be nearly equal. 



Fig. 2f. A portion of the surface of the shell enlarged. 



Position and locality. This species is found in the upper green shale of the group, more 

 abundantly than in any other position. It is likewise found in the Pentamerus limestone at 

 Rochester, Sodus, Wolcott, &c. 



444. 19. LEPT^NA PATENTA. 



Pl. XXI. Fig. 3 a, b, e. 



Shell resupinate, wider than high (about as ten to twelve, and varying as eleven to fourteen); 

 hinge-line apparently not extended beyond the width of the shell ; surface marked by fine 

 unequal striae, which are crossed by fine concentric lines ; concave (dorsal) valve with the 

 muscular impression foliated ; inner surface thickly covered with sharp points, which extend 

 into the muscular impression ; rays scarcely visible on the inside of the shell. 



This species closely resembles the L. subplana of the Niagara group, with which species I 

 had been inclined to unite it ; but it differs in the finer and more numerous rays, which are less 

 sharply elevated, and in the interior, which is nearly free from rays and very papillose, while 

 the interior of the Niagara species is strongly rayed and scarcely papillose at all. The propor- 

 tions of length and breadth are not greatly different in the two shells. 



Fig. 3 a. The interior of the concave valve, showing the muscular impression. 

 Fig. 3 b. The exterior of the concave valve of another individual. 

 Fig. 3 c. A portion of the surface enlarged. 



