192 CD. Walcott — Fauna of the ZTpper Taconic 



line and rather strongly convex ; the beak is subcentral and 

 curves toward the hinge line, but does not reach it; an oval 

 muscular scar is situated just within the pallia! line, at the sup- 

 posed anterior end; pallial line simple, continuous as far as 

 observed. 



The minute size and the fact that we have only the cast of 

 the interior of the valve, render it very difficult to determine 

 the correct generic relations of this shell. The nearly central 

 position of the beak distinguishes it from all known species of 

 Modiolopsis ; while the muscular scar and pallial line, with the 

 oval form, relates it to Modiolopsis carta of the Hudson River 

 formation. The discovery of the character of the hinge line 

 may place it in a genus of the Arcadas ; but, at present, I do 

 not wish to state more than that I think it is undoubtedly a 

 lamellibranchiate shell. With the possible exception of For- 

 dilla Troyensis, which, possibly, may be the shell of some 

 Estheria-like crustacean, I know of no true lamellibranchiate 

 shell in the Cambrian system of America, as defined in 1886. 

 (This Journal, vol. xxxiii, p. 147, 1886.) 



Formation and locality. — Cambrian. Limestone, interbedded 

 in shaly Taconic slate, on the roadside north of School-house 

 No. 4, in the northeast part of Whitehall, Washington County, 



n. y. 



LBPEEDITIA (I) DERMATOIDES, 11. Sp. 

 Plate I, figs. 13, 13 a. 



Outline of the valves, elongate, suboval, with the extremities 

 of the hinge line rounded, subangular ; moderately convex, 

 sloping more rapidly to the ventral than the dorsal margin ; in 

 many specimens, however, it is difficult to determine the ven- 

 tral from the dorsal margin, owing to their almost equal curva- 

 ture and similar rounding of the ends ; the hinge line is arched 

 and but slightly marked. It is difficult to determine the anterior 

 and posterior ends of the valves in many of the specimens, but 

 in others the narrower end is considered as the anterior, and a 

 small, round depression on the inner side of the valve places 

 the muscular scar well toward the posterior end. The scar is 

 barely visible on the outer surface. 



The test is finely punctate, and so thin that it wrinkled in 

 some instances like a membrane or skin. 



Length of undistorted specimen, 6 mm ; greatest height, 3"5 mm . 



The strongly punctate surface is so unlike that of all the 

 species referred to Leperditia that it may be that this species 

 should be referred to a distinct genus. 



In its punctate surface and general form it is unlike any 

 other species known to me. 



