98 SYSTEMATIC PALEONTOLOGY 



Superorder OSTRACODA. 

 Family CYTHERIDAE. 



Genus CYTHERE Miiller. 



Cythere clarkana n. sp. 



Plate XXXV, Figs. 1-10. 



Description. — Carapace rather irregular in outline but usually elon- 

 gate-ovate, about 1.30 mm. in length, 0.65 mm. high and 0.6 mm. thick. 

 Valve well rounded, the greatest convexity towards the posterior end, 

 unequal, the left overlapping the right at the cardinal angles and in 

 turn overlapped by the right along the ventral edge. Position of 

 anterior hinge teeth marked by an oblique dorsal swelling. Hinge 

 straight, the length being about three-fifths that of the entire carapace. 

 Left valve obliquely rounded posteriorly, most prominent in the lower 

 half ; ventral edge straight or slightly arcuate ; the posterior edge rather 

 narrowly rounded, the curve generally straightened in the upper half, 

 and the junction with the extremity of the hinge line sometimes ob- 

 tusely angular. In the right valve the ends are more equal in breadth 

 and curvature, although the ventral half of the anterior is also more 

 strongly curved, and the ventral outline is faintly sinuate instead of 

 arcuate. Surface of both valves coarsely reticulate, the meshes ar- 

 ranged somewhat concentrically about a subcentral point. The ridges 

 forming the raised part of the network bear, especially at their Junction 

 angles, spines, the size and number of which vary with age. In the 

 old condition, the surface is quite rough with these spines, the ridges 

 thicker and the reticulation less obviously concentric. The lower two- 

 thirds of the anterior and posterior margins of the left valve bear a 

 series of small spines but on the right valves such spines have been 

 observed only on the anterior edge and they are often wanting even 

 there. Edge view lanceolate with the ends a little blunt or truncate. 

 Hingement consists of a rather large anterior lateral tooth connected 

 by a bar with a somewhat smaller posterior tooth and corresponding 

 sockets in each valve. 



This striking and characteristic fossil is very abundant in the Calvert 

 formation at Plum Point. We know of no American species with 



