CHAPTER VI. 



Branch ARTHROPODA. 



Class CRUSTACEA. 



Sub-class EUCRUSTACEA. 



Super-order OSTRACODA. 

 Family OYTHERIDAE. 



Genus CythkrEis Jones. 



Cythereis bassleri Ulrich. 



Plate ex., Pigs. 1-3. 



1901. Cythereis bassleri Ulr., Md. Geol. Surv., Eocene, p. 117, 

 pi. 16, figs. 5-8. 



Description. — "Carapace oblong, length 0.80 to 0.85 mm., 

 widest and rounded anteriorly; the posterior edge more or less 

 angular in the middle, straight or slightly sinuate above to the 

 angular extremity of the hinge, and with two or three spines 

 projecting from the slightly convex, lower half; edges with a 

 thickened rounded rim, becoming obsolete near the center of 

 the flattened ventral region; hinge line straight, except at the 

 antero-cardinal angle, which is thickened and prominent; ven- 

 tral outline slightly sinuate. Valves equal, with a rounded sub- 

 central node, sometimes obscured by a network of small ridges, 

 and a sharp ventral ridge rising gradually from its inception at 

 the antero-ventral angle and ceasing abruptly at a point about 

 one-fourth of the length of the valve from its posterior extrem- 

 ity. A less prominent ridge runs from the high end of the ven- 

 tral ridge in a slightly oblique direction, to the post-cardinal 

 angle and then turns forward. The whole surface is covered 



(843) 



