112 SYSTEMATIC PALEONTOLOGY 



scarcely oblique, and almost uniformly curved; ventral margin gently 

 convex, the dorsal edge more arcuate, though the anterior extremity of 

 the hinge seems to be about midway between the obtuse postcardinal 

 angle and tlie anterior extremity of the valve. Surface with pits of 

 moderate size, rather widely separated and with no very evident ar- 

 rangement. 



Length of a left valve 0.88 mm., greatest height of same 0.55 mm., 

 greatest thickness of same 0.26 mm. 



Of this species we have seen only a single left valve, but as it is a 

 Maryland fossil and from an horizon from which comparatively few 

 OsTRACODA are known, and as other specimens of it will almost certainly 

 occur in our unpicked washings, we considered ourselves justified in 

 proposing a new name for it and offering a brief description in this work. 



In its general aspect this species reminds of Cytheridae, and to a less 

 extent of Xestoleheris, rather than Cythere, but on account of the shape 

 of its posterior end, in which it agrees with the two preceding species, 

 it has seemed best to refer it, at least provisionally, to the same genus. 

 For comparisons with other species see under C. shattucki. 



Occurrence. — Choptank Formation. Pawpaw Point. 



Collection. — IT. S. jSTational Museum. 



Cythere martini n. sp. 

 Plate XXXVI, Figs. 11-15. 



Dfiscription. — Carapace small, suboblong, widest anteriorly though 

 the difference between the heights of the two ends is variable and 

 sometimes does not exceed the difference between five and six. Eight 

 valve with a long, straight dorsal edge, terminating anteriorly and 

 posteriorly in rather distinct angles ; anterior edge with a thick border, 

 obliquely subtruncate, and usually with a fringe of short spines in the 

 middle and lower thirds; posterior outline sometimes uniformly curved, 

 backward from the anterodorsal angle and then forward again into the 

 nearly straight ventral margin, the curve into the latter being gradual. 

 More commonly, however, especiall}^ when the posterior fringe of five 

 or six spines is well developed, there is a small excision in the upper 

 third of the outline. Often a small prominence is noticeable about the 



