140 Systematic Paleontology — Middle Devonian 



times salient but often rounded. Ventral valve varying from moderately 

 to extremely convex, gibbous in the middle, rounded upon the umbo and 

 little elevated above the hinge-line, with beak small and scarcely in- 

 curved, while in some specimens a median ridge crosses the center of 

 the valve; cardinal area about a line in width, gently narrowing towards 

 the extremities, vertically striated, with the margin crenulated for more 

 than half the distance from the center to the extremities. Dorsal valve 

 usually almost flat or slightly concave in the upper and central portions, 

 suddenly deflected towards the margin, in some specimens regularly 

 concave; cardinal area very narrow and nearly linear throughout, striate 

 and crenulate as in the ventral valve. Surface of the ventral valve is 

 marked by sharply elevated, strongly crenulated striae, between which are 

 sometimes one or two less elevated striae similarly crenulated, and still 

 finer striae between the latter; in some specimens there are wider spaces 

 of finer equal striae between the stronger ones; and in other specimens 

 the striae are nearly all strong and sharply elevated, with few finer ones, 

 which soon rise to the strength of the others; close \indulating concentric 

 striae cover the whole surface ; the dorsal valve is marked by distant sharp 

 elevated striae, between which there are from three to six and rarely ten 

 finer striae, which are very finely crenulated by concentric striae; the 

 interior of the valves is finely pustulose. 



The Maryland collection contains a single, imperfect specimen of the 

 interior of a dorsal valve. A part of the strongly crenulated cardinal 

 area is shown, a portion of the muscular impression outside of which it 

 is strongly pustulose, and the pustules are larger in the central portion 

 of the shell before reaching the deflected part toward the margin. The 

 specimen appears somewhat like a large form of S. dcmissa (Conrad). 



Length, 37 mm.; width, 43 mm. 



Occurrence. — Eomney Formation, Hamilton Member. East bank 

 Evitts Creek below Wolfe Mill ( ?) ; on the Hancock-Harrisonville Eoad 

 about 2 miles north of Hancock. 



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

 American Museum of Natural Historv. 



