\M PALEONTOLOGY OF NEW YORK. 



1)1' the riirlit valvt' is k'ss (k'liiK'd tliaii in the Itft. iiiid the livssal sinus is a 

 little tU'oper. 



Test tliiii : s|n'ciiiii'iis partiallv t'xfoliatcd, or occiirrinu in tlic ciinditioii ol" 

 casts, show sliarpiv cU'valfd, laiiu'llosc, coiicciitric stri:v, w liidi arc scry dis- 

 tinct on the wings, and crowded and somewhat ("asciculate on the anterior 

 side and ear. No intermediate finer stria- have been ohserved. In well- 

 ])reserved specimens the sharj) lauielhe ha\e uiiduhitini;' margins. 



Interior nnknown. Ligamental area marked liy a single groove. 



A large specimen lias a length of 4.'] mm., height •')() nnn., hinge-line M7 mm. 

 Another example has a length of oli mm., height '■)'■'> mm., liingc-rnu' -JO mm. 

 In tlu' yoimgei- shells the height is proportionallv somewhat less than in 

 the older ones. 



This species, compared with the preceding, has a greater height of hody and 

 shoi'ter liinge-line. and ilill'ei's in the conspicnous, sharp, concentric lamella^. 

 Ill this species the concentric striie do not produce the folds and uudulatinns 

 wliich are characteristic of L. Rafinesquii and L. Greeni. 



Formation and localities. In shales of tlu' Hamilton group at Pratt's falls, 

 nudiidaga countv, and in the coarser beds at Schoharie, X. Y. 



'o" 



TiKllll'TKHIA MlT(lli:r,I,I. 



I'LATK X.X, KK;. s ; and I'I.ATE, I, XXXVIII, KIc, -Hi. 



Lewptma MitcheUi, Ham.. Pal. N. V., vol. v, pt. 1. Plates and Exi>laiiations : PI. ::0, li;,'. 8. Jan., 1883. 



Shell large, sul)-rhond)()idal ; body ovate, moderately oblique; height greater 

 than tiie length ; anterior nuirgin nearly vertical from the ear for about half 

 the height, then broadly curving to the post-basal side, thence more abruptly 

 bending, making the posterior eml slightl}^ extended. 



Left valve gibbous on tiie umbo, sloping IVom highly conxcx aboxc to 

 moderately convex below. Kight valve unknown. 



Hinge-line straight, i'(jual to the length of the valve. 



Beak anterior, acute, inclined forward, prominent. Lmbonal region prom- 

 inent, subtending au acute angle. 



