II i:i.i)i:i;r.i:i;i; Imikm \ iion in M\i;yi.ani) 17 



one of the most valuable faunal subzoiics of that member for the correlation 

 of the various sections of the State. 



Occurrence. — IIeldehbekg Formation, Keyser Member. Pinto, 

 Devil's Backbone, Corriganville, Cash A'alley, Market Street Bridge Cum- 

 berland, Breakneck Hill, I] miles northeast of Flintstone, Flintstone, 

 Hancock, Hazen, Maryland; Keyser, West Virginia; ITyndmnn, Pennsyl- 

 vania. 



CoUection. — .Maryland ( icological Siir\ey. 



(IvpiDrLA (Sik]5i:ri:lla ) coky^caxknsis \.\\\. couRUiAXEXSis n. var. 

 Plato LXII, Figs. 12-18 



Description. — Shell somewhat transversely subelliptical in outline, 

 wider than long. A'entral valve convex, gibbous, greatest convexity about 

 two-thirds the distance from the front to the beak; beak incurved over that 

 of the opposite valve. The median portion of the valve is elevated in some 

 individuals to form a fairly w^ell-defined fold which extends from a short 

 distance anterior to the umbo to the front, and contains several incon- 

 spicuous plications, while in other individuals the fold is very faint. On 

 each side of the median fold there are two to three simple plications which 

 are most prominent at the front and become obsolete from the center of 

 the shell to the beak, leaving this portion of the shell smooth. Dorsal 

 valve transversely subelliptical in outline, convex, greatest convexity just 

 anterior to the umbo; much less convex than the ventral valve. It pos- 

 sesses a more or less depressed mesial siinis which never extends posterior 

 to the center of the shell, and which is bounded by two rounded plications. 

 One or two plications occur on each side of the sinus. Both valves are 

 marked by inconspicuous concentric lines of growth. Dimensions: 17 

 ram. long and 19 mm. wide. 



This species closely resembles Gypiclula anguUda AVeller from the 

 Coeymans of Xew Jersey from which it differs as follows: The median 

 portion of the shell is elevated into a fold which is rarely sharply defined 



