256 Systematic Paleoxtology — Middle Devonian 



Mytilarca oviformis Clarke. 1903, N. Y. State Mus., Bull. 65, p. 457. 

 Plethomytilus oviformis Grabau and Shimer, 1909, N. Am. Index Fossils, 

 vol. i, p. 434, figs. 567d, e. 



Description. — "Shell large; body ovate, erect, wide posteriorly and 

 acute above ; length about one-fifth greater than the height ; ventral mar- 

 gin for nearly half the length of the shell nearly direct, thence gently 

 curving into tlie posterior extremity which is broadly rounded; dorsal 

 margin very gently curved. Valves equal, regularly convex in the pos- 

 terior part, becoming gibbous in the umbonal region ; hinge-line straight, 

 less than the height of the shell; beaks prominent, anterior acute, and 

 incurved, rising above the cardinal line. Test thick, marked by fine, 

 close striae of growth which at intervals are fasciculate and raised into 

 lamellose ridges and very much crowded and elevated on the ventral side 

 of the shell; ligamental area wide, finely striated longitudinally." 

 Hall, 1884. 



Several broken specimens were found the fonn of which and other char- 

 acters apparently leave no doubt regarding their identity with the above 

 species. A large specimen from western Maryland, the exact locality 

 unknown, was sent to Dr. Grabau who wrote as follows : " I have a 

 specimen (internal mold) of Plctltoimjtilus oviformis from the Encrinal 

 limestone of Eighteen !Mile Creek [X. Y.] which is of the same size as 

 this specimen. Placed side by side they appear to be perfectly identical, 

 the differences being such as can easily be accounted for by the fragments 

 broken away on your specimen." The species is well defined by its large 

 size, ovate outline; truncate front; wide ligamental area; and beaks pro- 

 jecting above the cardinal line. 



Length, 58 + mm. ; too badly broken to determinate the height. 



Length, of a smaller specimen, 45 mm. ; height, 33 mm. 



Occurrence. — Eomney Formation, Hamilton Member. East l)ank 

 Evitts Creek below Wolfe :\nil ; cut on B. & 0. E. E. cut at 21st Bridge; 

 along Flintstone Creek in Gilpin; western Maryland, but exact locality 

 unknown. 



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

 American Museum of Natural History. 



