254 Systematic Paleontology — Middle Devonian 



lateral, with a strong angular fold along the middle, separated from the 

 body of the valve by a distinct rounded sulcus and broad byssal sinus; 

 margin rounded; extremity obtuse. Wing triangular, flat, limited by 

 the post-umbonal slope ; margin concave ; extremity acute. Test thin, 

 marked with distinct concentric striae of growth, which are crowded and 

 conspicuous on the wings. There are often obscure traces of radii, which 

 are more distinct on the wing in casts or exfoliated specimens. Liga- 

 mental area narrow, with a single distinct groove. Some specimens 

 apparently indicate the existence of an oblique lateral tooth on the 

 posterior side of the umbo." 



The writer's specimen is smaller than those described by Hall, the 

 height of the shell being only 5 mm. and the length of the hinge-line 6 mm. 



Occurrence. — Romney Forjiation, Onondaga Member. Williams 

 Road, 31 2 miles southeast of Ciimberland. 



Collection. — U. S. National Museum. 



[E. M. Kindle.] 



Genus LEPTODESMA Hall 



Leptodesma rogersi Hall 

 Plate XXIX, Figs. 7-10 



Leptodesma rogersi Hall, 1883, Pal. N. Y., vol. v, pt. i, plates and explanations, 



pi. xxi, figs. 1-9. 

 Leptodesma rogersi Hall, 1884, Pal. N. Y., vol. v, pt. i, Lamellibranchiata i, 



p. 176, pi. xxi, figs. 1-9. 

 Leptodesma rogersi Clarke, 1903, N. Y. State Mus., Bull. 65, p. 419. 

 Leptodesma rogersi Grabau and Shinier, 1909, N. Am. Index Fossils, vol. i, 



p. 426, fig. 556b. 



Desci'iption. — Shell of small or medium size, subrhomboidal ; body 

 ovate, very oblique; length greater than the height; anterior and basal 

 margins broadly rounded; posterior margin extended and abruptly re- 

 curved. Valves equally convex above; right one somewhat depressed be- 

 low, comparatively higher than the left. Hinge-line straight, longer 

 than the length of the shell. Beaks subanterior, obtuse, nearly erect, 

 prominent, umbonal region gibbous, oblique. The anterior extremity is 

 scarcely alate or aurieulate, consisting of a rounded extension, straight 



