188 PAL/EONTOLOGY OF NEW YORK. 



A specimen of a left valve has a lenjrth of 10 iiiiii., iieiiiht T.o nun., iiiniic- 

 line alioiit 111 mm. A similar specimen lia.< a Icnirth of 11 mm., liei<i;ht G.5 

 mm., and hinge-line about 11 mm. A rii;ht valve has a length of '.I nun., 

 height (') mm., hinge-line about S mm. iVnother one has a length of lii mm., 

 height 11 mm., hinge-line about Ki mm. 



This is a small and aliuiidaiit species, often occurring in great inimbers on 

 the surfaces of A\:\\\- lavers. It is distinguished hv its form and the rescular 

 lamellose appearance ol' the surface. 



Formation and localities. In tiie shales of the Chemung group at Connewango, 

 Cattaraugus county; Nanticoke Springs, Broome county, and south of Ithaca, 

 N. Y. 



LkPTODES.M.V I'OTENS. 



I'I,.\TE X.\I, KKiS. 21, »); PI..\TK XXU, KU;> M, IJ. 1(1, (in?) ■>! ; axd PLATE LXXXI.X. KILJ. 7 



LeptiidfrSinu jMitens. H.ai.l. Pal. N. V., vol. v, jit. 1. Plates and Exiilanaticns : PI. 21. lifrs. -Jl. 8(1; |il. 2l'. 



tig-s. 11. 1.'. H). 21. .Jan.. ISSS. 



iSiiELi, large, sub-rhomboidal ; body ovate, oblicpie, l)road IjcIow: length more 

 than one-third greater than the height ; ante-byssal margin sub-truncate, 

 erect, ()l)li([ue below, basal margin broadly curving ; posterior margin broad, 

 extended and abruptly recurving at the upper extremity. 



Left valve convex, gibbous al)()ve ; the greatest convexity at one-third the 

 height of the shell from the beak. Kigiit valve almost e(|ually convex, more 

 alii'ujitly gibbous on the uml)o. and coinparatively shorter and wider. 



Hinge-line straight, about e(|ii;d to the length of tlie shell. 



Beak sub-anterior, obtuse, erect, prominent, arching over the hinge. 

 Umbonal region gibbous, very prominent, limitt-d anteriorly by a shallow 

 depression extending from a point anterior to the beak to the margin at one- 

 third the height of the shell below the hinge-line; posterioily limited by the 

 abrupt post-cardinal .slope. Uinlion.d angle acute. 



Anterior extremity extended and angular. \\ ing large, trianguhir, joining 

 the body near the posterior extremity, distinctly limited ; margin l)roadly 



