L66 PALEONTOLOGY OF NEW YORK. 



of the right valve is less defined than in the left, and the byssal sinus is a 

 little deeper. 



Tesl thin : specimens partially exfoliated, or occurring in the condition of 

 casts, show sharply elevated, lamellose, concentric stria', which arc very dis- 

 tinct on the wrings, and crowded and somewhat fasciculate on the anterior 

 side and ear. No intermediate liner stria' have been observed. In well- 

 preserved specimens the sharp lamellae have undulating margins. 



Interior unknown. Ligamental area marked by a single groove. 



A large specimen has a length of 43 mm., height 50 nun., hinge-line 37 mm. 

 Another example has a length of 32 mm., height 33 nun., hinge-line 30mm. 

 In the younger shells the height is proportionally somewhat less than in 

 the older ones. 



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

 shorter hinge-line, and diners in the conspicuous, sharp, concentric lamella'. 

 In this species the concentric stria 1 do not produce the folds and undulations 

 which are characteristic of L. Rafinesijidi and L. Greeni. 



Format/on and localities. In shales of the Hamilton group at Pratt's falls. 

 Onondaga county, and in the coarser beds at Schoharie, N. Y. 



Lkiopteria Mitchelli. 



PLATE \X. Hi. «. i\n PLATE, I.XXWIII. FIG *: 

 I pteria Mitchelli, Hall. Pal. N. V.. vol. v. pt. 1. Plate? ami Explanations: PI. SO, fig. 8. Jan.. 1>^:: 



Shell large, sub-rhomboidal ; body ovate, moderately oblique ; height greater 

 than the length; anterior margin 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 end slightly extended. 



Left valve gibbous on the umbo, sloping from highly convex above to 

 moderated) convex below. Right valve unknown. 



Hinge-line straight, equal to the length of the valve. 



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

 inent, subtending an acute angle. 



