Maryland Geological Survey 317 



Several well defined specimens of this species were found in the Hamil- 

 ton shales of Washington County. It is an easily recognized species from 

 its elongate form, parallel dorsal and ventral margins, umbonal ridge and 

 furrow, ridge and furrows on cardinal slope and the conspicuous undula- 

 tions of the anterior end and cardinal slope. 



Length, 33-45 -|- mm. ; height, about 12 mm. at posterior extremity. 



Occurrence. — Eoainey Formatiox, Hamilton Member. B. & 0. 

 R. E. cut at Hancock Station, W. Ya. 



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

 American Museum of Natural History. 



Orthonota (?) parvdla Hall 

 Plate XXII, Figs. 1, 2 



Orthonota pnrvula Hall, 1870, Prelim. Notice Lamellibranchiata 2, p. 88. 

 Orthonota (?) parvula Hall, 1885, Pal. N. Y., vol. v, pt. i, Lamellibranchiata 



ii, p. 482, pi. Ixv, figs. 2, 3; pi. Ixxviii, figs. 29-32. 

 Orthonota (?) parvula Clarke, 1903, N. Y. State Mus., Bull. 65, p. 468. 



Description. — " Shell small, elongate subtrapezoidal ; length three 

 times the height; ventral and dorsal margins straight and subparaJlel; 

 posterior extremity vertically or obliquely truncate below and curving 

 forward above; anterior end narrowly and regularly rounded from the 

 cardinal margin. Valves moderately convex below and posteriorly, becom- 

 ing gibbous in the middle and umbonal regions; beaks at about the 

 anterior fourth, flattened and incurved, rising very little above the hinge- 

 line; umbonal slope angular, extending to the post-inferior extremity; 

 post-cardinal slope flat or slightly concave; sometimes obscurely marked 

 by a depression or fold below the middle. Surface marked by extremely 

 fine, thread-like concentric striae, which are often lamellose on the post- 

 cardinal slope." Hall, 1885. 



The blue shales of Evitts Creek below Wolfe Mill have furnished a few 

 clearly marked specimens of this easily recognized species, although 

 smaller than the average of those found in New York. Its most marked 

 characters are the elongate, subtrapezoidal form ; straight ventral and 

 dorsal margins ; angular umbonal ridge ; flat to slightly concave post- 



