332 Systematic Paleontology 



ably prove tliis form to be a distinct species." This fossil was collected at 

 Cumberland, Maryland, by Hall and is cited from the rocks of the Lower 

 Helderberg. The individual at hand consists only of the brachial valve. 



Brachial valve transversely subelliptical in outline, wider than long, 

 extremely convex, gibbous, greatest convexity about 3 mm., anterior to the 

 beak, sloping somewhat abruptly to the lateral margins, there becoming 

 plane to concave. Hinge-line straight and less than the greatest width 

 of the shell. Lateral and front margins rounded ; beak strongly incurved. 

 A somewhat shallow sinus extends from the beak to the front, gradually 

 becoming broader from the beak anteriorly. Surface marked by well- 

 defined simple tubular ribs which increase by interstitial addition and 

 implantation. 



Dimensions : Length 17 mm. ; width 23 mm. 



This species differs from Schiichertella defortnis in (1) having the 

 dorsal valve extremely convex, (2) being transversely subelliptical in out- 

 line while S. deformis is suborbicular lenticular, (3) having a well-defined 

 sinus in the dorsal valve. 



Occurrence.- — Helderberg Formation, Keyser Member. Devil's 

 Backbone. Beneath the Gypidula coeymanensis var. prognostica zone. 



Collections.— TI. S. National Museum, American Museum of Natural 

 History. [Maynard.] 



Sohuchertella marylandica n. sp. 



Plate LXI, Figs. 5-9 



Description. — Shell plano-convex, subelliptical in outline. Length 

 greater than the width. Lateral and anterior margins rounded. Hinge- 

 line straight, about two-thirds the greatest width of the shell. Cardinal 

 area high, triangular in outline. Pedicle valve convex, ventricose along 

 the median portion and descending rather abruptly towards the lateral 

 margins. Greatest convexity about 7 mm. anterior to the beak, beak only 

 slightly incurved, prominent, and extending high above the beak of the 

 dorsal valve. 



