lis SYSTEMATIC PALEONTOLOGY 



much thicker than the other; end view subovate. Valves compara- 

 tively thin for this genns, the marginal groove of the right valve rela- 

 tively narrow though sharply defined. Interior of right valve with two 

 subovate smooth spaces, situated one in the anterior, the other in the 

 posterior half, and around them concentric roAvs of small pustules. Sur- 

 face smooth or minutely punctate. 



No known Tertiary species agrees very closely with this. The well- 

 known C. compressa (Miinster), has a similar edge view, as have also 

 several other species, but otherwise, the form of its carapace, especially 

 the ventral portion of the outline, is quite different. The Cretaceous 

 C. ovata is probably a closer relative but differs obviously in its edge 

 and end views. 



Occurrence. — Aquia Formation. UpjDer Marlboro. 



Collection. — Maryland Geological Survey. 



Cytherella submarginata n. sp. 

 Plate XVI, Figs. 14, 15. 



Description. — Carapace about 1.0 mm. in length, somewhat oblong, 

 rounded at the ends, the posterior end a little wider and its margin 

 more oblique above and merging more gradually into the very slightly 

 arcuate dorsal outline than the anterior; ventral margin straight, edge 

 view subcuneiform, end view subovate. A^alves compressed convex, 

 thickest posteriorly, with an obscurely defined broad depression near 

 the midlength and mostly above the center of the valves. A narrow 

 but distinct rim borders the two ends. Surface smooth. 



Of this species only the single valve figured has been seen. Com- 

 pared with described species it was found to agree rather well with C. 

 londinensis Jones a Lower Eocene species from London, Eng., but after 

 a closer examination it was decided that it could not be justly referred 

 to that species. As described and figured C. londinensis must have quite 

 a different appearance in edge views, due to the more uniform convexity 

 of its valves. The central depression and marginal rims as well as its 

 different outline, will serve to distinguish C. svhmarr/iiiata at once from 

 C. marlho7-oensis with which it is associated. 



Occurrence. — Aquia Formation. Upper Marlboro. 



Collection. — Marvlaud Geological Survey. 



