MARYLAND GEOLOGICAL SURVEY 103 



be noticed that in C. pleheia the ends are more sharply curved, and the 

 anterior margin often obliquely subtruncate, with the greatest promi- 

 nence nearer the ventral edge. Finally, the posterior extremity of the 

 right valve is narrower and a less oblique. 



Length 1.1 mm. to 1.15 mm., height 0.54 mm. to 0.57 mm., thick- 

 ness 0.5 mm. to 0.52 mm. 



Occurrence. — Calvert Formation. Plum Point. Chesapeake Group. 

 James Eiver and Yorktown, Va. 



Collections. — U. S. National Museum, Maryland Geological Survey. 



Cythere plebeia var. modica n. var. 

 Plate XXXV, Figs. 18, 19. 



Description. — This variety, of which only left valves are known, is 

 distinguished from the typical form of the species by its shorter and 

 more ovate form. The surface pits also constitute a more conspicuous 

 feature. 



Occurrence. — Calvert Formation. Plum Point. 



Collections. — U. S. National Museum, Maryland Geological Survey. 



Cythere plebeia var, capax^ n. var. 

 Plate XXXV, Figs. 30-33. 



Description. — This variety is distinguished from the typical variety 

 by its greater height and finer surface pitting. The latter, in all the 

 specimens seen, is restricted to the postcentral region of the valves. 

 The outline of the right valve, furthermore, is more arcuate in its 

 ventral and dorsal portions, while the posterior extremity is no less 

 sharply rounded. 



Occurrence. — Calvert Formation. Plum Point. 



Collections. — U. S. National Museum, Maryland Geological Survey. 



Cythere burnsi n. sp. 

 Plate XXXVI, Figs. 34-39. 



Description. — This well marked species agrees in many respects with 

 the associated C. incequivalvis and C. pleieia, the dorsal half of the 

 outline, especially of the left valve, being much as in the former, while 



