Maryland Geological Survey 655 



Cypricardella gregaria Grabau and Shimer, 1909, N. Amer. Index Foss., vol. 

 i, p. 535. 



Description. — Shell rhomboid-ovate, broadest posteriorly; hinge-line 

 straight and more than half the length of the shell; posterior margin 

 sloping, lower margin siibtransverse ; beaks anterior; valves depressed 

 convex; surface smooth or M-ith fine concentric lines. 



This species lends itself to ready recognition by its slight convexity 

 and smooth valves, in which respects it may be distinguished from the 

 common member of the genns, C. hellistriata. C. gregaria occurs occa- 

 sionally in the Ithaca fauna of Xew York and is locally abundant in the 

 Chemung fauna. 



Length 20 mm. ; height 14 mm. 



Occurrence. — Jennings Formation, Parkhe-id ? Member. In 

 blocky argillaceous sandstone, 5 miles west of Piney Grove on west side 

 of Green Eidge, Allegany County. 



Collection. — Marvland Geological Survey. 



CvrRICARDELLA GREGARIA (Hall) Var. 



Description. — The specimens referred to this variety do not differ in 

 proportions from the typical C. tenidstriata of Maryland, but they are 

 usually smaller, while the surface is without distinct elevated striae. They 

 differ from C. gregaria in being proportionally longer, umbonal slope not 

 angular, posterior extremity less oblique, convexity slight. 



Length 30 mm.; height 18 mm. 



Occurrence. — Jennings Formation, Chemung Member. Allegany 

 Grove, 1750, 2662. Parkhead Member. Williams Eoad, on Polish 

 Mountain, 1352: 2 miles north of mouth of Town Creek, 1282, 1642; 

 4 miles southeast of Pratt on White Surphur Branch; Town Creek, 1679, 

 1851; 2 miles west of Pawpaw, West Virginia, 1763; Berkeley Springs, 

 West Virginia, 1554 to 1566. A variety occurs in the Parkhead at Mill- 

 stone at 1772, which is more elongate, its inferior-anterior angle more 

 produced. 



Collection. — Maryland Geological Survey. 



