MARYLAND GEOLOGICAL SURVEY 137 



This is the most fragile of the Ostracoda occurring in the Plum Point 

 washings. Its valves are always separated and they are not only difficult 

 to mount without breaking, but, on account of the approximate quality 

 of their ends, it is also difficult to distinguish the right from the left. 

 The obtuse, subequal ends, the cylindrical form fragile test and reticu- 

 late ornament constitute a combination of characters not possessed by 

 another species of the genus known to us. It is probably nearest our 

 Cytlierideis longula. 



Length 0.9 mm., greatest height 0.37 mm. 



Occurrence. — Calvert Formation. Plum Point. (ISTot common.) 



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



Cytherideis sub^qualis n. sp. 

 Plate XXXVII, Fig. 28. 



Description. — Carapace' elongate subreniform, with rounded, approxi- 

 mately equal ends, distinctly arcuate dorsum and slightly sinuate ven- 

 tral outline. Left valve overlapping the right along the ventral margin. 

 Test strong, surface sparsely pitted. 



The general aspect of the closed carapace of this species is decidedly 

 like that of a Bythocypris, and we deem it quite possible that its rela- 

 tions are with that family rather than the Cytheridce. Still, considering 

 the rather close agreement in external characters exhibited between it 

 and the following two species, whose hingement is known to be in ac- 

 cordance with that of Cytherideis, we have considered ourselves justified 

 in assuming provisionally that the same type of hingement pertains also 

 to C. subcequalis. Compared with described Tertiary species there is 

 none known to us from which it may not be distinguished with ease. 



Length 0.88 mm., height 0.37 mm., thickness 0.35 mm. 



Occurrence. — Calvert Formation. Plum Point (Pare). 



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



Cytherideis semicircularis n. sp. 



Plate XXXVII, Figs. 18-20. 



Description. — Carapace nearly semicircular in outline, the ventral 

 border straight, the ends abruptly rounded. Left valve the larger, form- 



