LAMELLIBRANCHIA TA. 183 



byssaJ sinus, limited by an oblique depression which reaches to near the 

 middle of the length of the valve. Wing small, joining the bod} below the 

 middle ; margin oblique below and abruptly concave just beneath the cardinal 

 line, recurving and produced into a short spiniform extension. The righl 

 valve is less convex, the wing larger and more extended along the posterior 

 slope. 



Test thin, marked by fine, distant, lamellose striae with intermediate finer 

 lines. The stronger striae are more conspicuous on the anterior. The 

 partial casts are nearly smooth. 



Interior unknown. 



( hie 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 stria^ 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 ■:•-'. r, 



Avicula protexta, Conrad. Jour. Acad. Nat. Sci., Phila., vol. viii, p. 23S, pi. 12, fig. 6. 1S4L'. 

 Pterinea protexta (Conbad), S. A. Milleb. Cat. Amer. Pal. Fuss., p. 202. ls77. 



Lrptodesmd protextwm (Conbad), Hall. Pal. N. Y., vol. v. pt. 1. Platesand 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 bvssal sinus, oblique : 

 base broadly rounded and abruptly recurved on the post-basal extremity. 



Valves 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. 



