LAMELLIBRANCHIA TA. 189 



sinuate; extremity produced into a strong spine (the extent of which is 



unknown). 



Surface marked by strong concentric lines of growth, which are crowded 

 into small fascicles at irregular intervals on the body of the shell, and become 

 lamellose expansions on the anterior. On the wing they appear as sharp 

 equidistant lamellae. Casts of the interior show the concentric strise in a 

 subdued condition. 



Interior unknown. 



The largesl left valve observed has a length, measured from beak to base, 

 of 62 mm., height 4G mm., hinge-line, exclusive of the spine, 58 nun. A 

 smaller specimen has a length of 57 mm., height 39 mm., hinge-line, to base 

 of spine, 58 mm. A right valve referred to this species has a length of 36 

 mm., height 28 mm., and hinge-line, to base of spine. 35 mm. 



This species more nearly resembles L. robustum than any of the forms here 

 described ; hut it is larger, the wing proportionally larger anil distinctly limited, 

 and the sinus of the wing more central. The right valve is also more convex 

 and the wing more deeply sinuate. It occurs in the upper members of the 

 Chemung group, associated with Spirifera Verueuili, while L. robustum is found 

 only in the middle of the series. 



It is a larger and more robust shell than L. Mortoni, and the right valves 

 are very unlike. 



Formation and localities, in the Upper Chemung group at Olean, Portville, 

 Cassadaga lake, and in loose specimens collected near Panama, X. Y. 



Leptodesma potexs, var. juvexs. 



PL \TE XXII. PIG. IB. 



Leptodesma i><>tfn-<. r<<,- juvens, H.u.r.. Pal. N. Y.. vol. v, ]>t. 1. Plates and Explanations: PI. 22. fig. I''.. 



Jan., 1SS3. 



Shell small, rhomboidal ; body ovate, oblique; the greatest length more than 

 once and a half the height : anterior margin oblique, very broadly curving 

 below : post-basal extremity rounded and abruptly recurved. 



Left valve convex below, very gibbous and ventricose in the middle and 

 above. Right valve unknown. 



