MARYLAND GEOLOGICAL SURVEY 327 



middle of the base conspicuously insinuate; surface sculptured with 

 crowded, rather prominent incremental lines, feebler towards the an- 

 terior end, which shows some faint radial markings; hinge-plate narrow, 

 left valve with a prominent subumbonal tooth and a feeble lamella a 

 little in front of it, a strong resiliary scar, and a minute, obsolete, very 

 distant posterior lamella; right valve with an arcuate, short, umbonal 

 lamina, a deep pit for the opposite cardinal above it, and a short, dis- 

 tant, sharp gro'ove corresponding to the posterior lamella of the opposite 

 valve; interior of the valves polished, faintly radially striate, the ad- 

 ductor scars rather low down. 



" This species is especially characterized by its relatively acute an- 

 terior end, which, in all the individual variations noted, is still pre- 

 served." Dall, 1900. 



Length, 6 mm.; height, 4 mm.; diameter, 3 mm (Dall). 



Occurrence. — St. Mary's Formatton. St. Mary's Kiver. 



Collection. — Maryland Geological Survey. 



Family LEPTONID/E. 



Genus ERYCINA Lamarck. 



Erychsta calvertensis n. sp. 

 Plate LXXXVII, Fig. 16 



Description. — ^Shell nearly ovate, base well arched and meeting pos- 

 terior margin in a curve above the line of the base ; anterior side slightly 

 produced, beak rather prominent; anterior and posterior dorsal margins 

 declining from the beak at an obtuse angle; teeth prominent; interior 

 with muscle impressions and pallial line distinct; exterior smooth; shell 

 depressed, thin. 



Length, 4 mm.; height, 3 mm.; diameter. 0.8 mm. 



Occurrence. — Calvert Formatiox. Plum Point. 



Collection. — U. S. National Museum. 



Erycina pruna n. sp. 



Plate LXXXVII, Fig. 17. 



Description. — Shell small, short, ovate, depressed; beak slightly pro- 

 jecting; inequilateral, anterior end the longer; anterior and posterior 



