Maryland Geological Survey 631 



Occurrence. — Jennings Fok^aiation, Genesee ^Iember. Near Wolfe 

 Mill, Gilpintown. 



Collection.- — ^^laryland Geological Survey. 



LUNULICARDIUM CYMBULA sp. nov/ 



Plate LXII, Fig. 4 



Description. — This species is distinguished by its transverse form and 

 central nmbo, the latter feature making the hiatus of about the same 

 length as that of the hinge-line on the other side of the beak. In this 

 respect the shell presents a quite unusual aspect, not indeed otherwise 

 noted among these species. The transverse diameter of the shell is 1% 

 times its length. The surface is very finely lined as in P. encrinitum 

 though the number of riblets is not so great. 



Length 5 mm. ; height 3 mm. 



Occurrence. — Jennings Formation, Genesee Member. Near Cor- 

 riganville where it is associated with Paracardium doris, Tornoceras uni- 

 anffulare, Pterocluenia fragilis, etc. 



CoUection. — Mar}'land Geological Survey. 



Genus PTEROCHAENIA Clarke 

 PlerocJicenia is distinguished from LunuUcardium by the fact that the 

 hiatus is anterior and the sicse are in their normal condition extended 

 outward and iipward in the form of long narrow wings. These aliform 

 siege are broad and convex near the beaks, narrowing rapidly downward; 

 they are separated from the body of the valve by a deep and narrow 

 double groove extending to the apex and enclosing a low ridge. In 

 LunuUcardium. the siege are normally vertical and much thickened; in 

 Pterochienia they are always thin and their surface lines are continued 

 directly from those on the body of the shell. Beneath the beak there is 

 no triang-ular striated area as in the genera referred to and no ligamental 

 striiB or articular processes are discernible. The surface of the valves is 

 smooth; when well retained onlv concentric striiu are apparent but slight 



' See N. Y. State Mus., Mem. vi, 1904, p. 212. 



