LAMELLIBRANCHIA TA. 
183 
byssal sinus, limited by an oblique depression which reaches to near the 
middle of the length of the valve. Wing small, joining the body below the 
middle ; margin oblique below and abruptly concave just beneath the cardinal 
line, recurving and produced into a short spiniform extension. The right 
valve is less convex, the wing larger and more extended along the posterior 
slope. 
Test thin, marked by fine, distant, lainellose striae with intermediate finer 
lines. The stronger striae are more conspicuous on the anterior. The 
partial casts are nearly smooth. 
Interior unknown. 
One specimen has a length of 29 mm., height 23 mm., hinge, to base of spine, 
15 mm. Another example has a length of 26 mm., height 19 mm., hinge, to 
base of spine, 15 mm. 
This species bears a general resemblance to L. spinigerum, with which it is 
sometimes associated, but the body is more erect and much wider below; the 
wing is somewhat wider, the spine shorter, and the striae less strongly marked. 
Formation and locality. In the middle portion of the Chemung group, on the 
Chemung river, between Elmira and Waverly, N. Y. 
Leptodesma protextum. 
PLATE XXI, FIGS. 22, 23. 
Avicula protexta, Conrad. Jour. Acad. Nat. Sci., Phila., vol. viii, p. 238, pi. 12, fig. 6. 1842. 
Pterinea protexta (Conrad), S. A. Miller. Cat. Amer. Pal. Foss., p. 202. 1877. 
Leptodesma protextwn (Conrad), Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 21, figs. 22, 
23. Jan., 1883. 
Shell small, sub-rhomboidal; body elongate-ovate, very oblique; length nearly 
twice as great as the height; anterior margin below the byssal sinus, oblique ; 
base broadly rounded and abruptly recurved on the post-basal extremity. 
Yalves sub-equally convex; the greatest convexity is above the middle of 
the length, becoming less toward the posterior side, which is somewhat 
depressed. The right valve is apparently a little smaller than the left. 
Hinge-line straight, about equal to the length of the shell. 
