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 striae in a 
subdued condition. 
Interior unknown. 
The largest left valve observed has a length, measured from beak tQ base, 
of 62 mm., height 46 mm., hinge-line, exclusive of the spine, 58 mm. 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; but it is larger, the wing proportionally larger and 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, N. Y. 
Leptodesma potens, var. juvens. 
PLATE XXII, FIG. 1C. 
Leptodesma potens, var. juvens, Hall. Pal. N. Y., vol. v, pt, 1. Plates and Explanations: PI. 22, fig. 16. 
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. 
