Maryland Geological Sukvey 605 



extending from the beak for one-half the length of the valve." Hall, 

 1867. 



Length 17 mm.; width 20 mm. 



Occurrence. — Jennings Formation, Chemung Member. Allegany 

 Grove, 29il. 



Collection.- — Maryland Geological Survey. 



Genus MERISTELLA Hail 

 Meristella humilis n. sp. 



Description. — Shell broadly ovate, widlh somewhat greater than length, 

 umbo prominent, hinge-line short. Ventral valve convex, point of great- 

 est convexity posterior to middle; depressed in front to form a shallow 

 sinus; slightly concave towards lateral margins, greatest width near mid- 

 dle. Beak nearly straight, projecting beyond that of dorsal valve. A 

 slightly angular ridge extends from beak to extremity of hinge, the sur- 

 face between it and hinge being flattened or concave.. Dorsal valve broadly 

 ovate; bearing a low fold towards front; point of greatest convexity pos- 

 terior to middle; beak small. 



Cast of interior shows two short dental lamellae in ventral valve and a 

 median septum extending nearly one-third length of shell in dorsal 

 valve, two depressions marking position of teeth. 



Surface smooth with faint concentric lines of g-rowth. 



Length of largest individual observed 10 mm. ; width VI mm. ; thick- 

 ness 4 mm. Only a few individuals have been seen. This species seems 

 quite distinct from any previously described form of the genus. 



Occurrence. — Jennings Formation, Woodmont Member, Ithaca 

 Fauna. Millstone, 795; Yellow Springs, West Virginia. 



Collection. — Maryland Geological Survey. 



