262 Systematic Paleoxtology — Middle Devonian 



posterior end, with a curved to obliquely truncate posterior margin ; auri- 

 culate anterior margin, the ear defined by a distinct sulcus; and curved 

 radiating striae. 



Length, 10-15 mm.; height, 7-10 mm. 



Occurrence. — Eomney Formation, Hamilton Member. Williams 

 Eoad 3 J miles southeast of Cumberland; east bank Evitts Creek below 

 Wolfe Mill; Williams Eoad \ mile east of Queen City Hotel, Cumber- 

 land; W. Va. side Potomac Eiver about 3 miles south of Cumberland; 

 W. Va. side Potomac Eiver -1 miles south of Cumberland; hill 3 miles 

 south of Cumberland. 



Collections. — Maryland Geological Survey; New York State Museum; 

 American Museum of Natural History. 



Superfamily NAIADACEA 

 Family CARDINIIDAE 



Genus NYASSA Hall 



jSTyassa arguta Hall (?) 

 Plate XXXI, Fig. 6 



Nyassa arguta Hall, 1870, Prelim. Notice Lamellibranchiata 2, p. 28. 

 Nyassa arguta Hall, 1885, Pal. N. Y., vol. v, pt. i, Lamellibranchiata ii, p. 



354, pi. liii, figs. 7-20. 

 Nyassa arguta Clarke, 1903, N. Y. State Mus., Bull. 65, p. 467. 

 Nyassa arguta Grabau and Shiraer, 1909, N. Am. Index Fossils, vol. i, p. 478, 



fig. 639. 



Description. — Shell of medium to large size, elongate subelliptical or 

 ovate-arcuate ; leng-th about twice the height ; basal margin nearly straight, 

 often slightly arcuate or contracted posterior to the middle, abruptly 

 recurved at the post-inferior extremity; posterior margin curved or ob- 

 liquely subtruncate; cardinal line gently arciaate; anterior end narrowed 

 and abruptly rounded. Valves depressed below, gibbous above and in the 

 umbonal region; beaks subanterior, small, closely appressed, rising but 

 little above the hinge-line; umbonal ridge prominent, rounded or sub- 

 angular, arcuate, extending to the post-inferior extremity; below and 

 parallel with the ridge there is a flattening or depression of the shell ex- 



