136 SYSTEMATIC PALEONTOLOGY 



Genus CYTHERIDEIS Jones. 



Cytherideis ashermani n. sp. 

 Plate XXXVII, Figs. 10-16. 



Description. — Carapace moderately elongate, considerably wider pos- 

 teriorly than anteriorly; ventral outline nearly straight, ends narrowly 

 rounded and most prominent beneath the midheight, above curving to- 

 ward the cardinal edge which is more gently arcuate. Ventral edge of 

 right valve slightly sinuate. Surface rather coarsely punctate, the 

 punctse having no very striking arrangement though they often form 

 irregular rows on the dorsal slope. On the longer specimens they con- 

 stitute less of a feature than on the smaller examples. 



Hingement consisting of a slight central overlap by the right valve 

 and thin terminal bars that fit into corresponding sulci in the cardinal 

 edge of the left valve. 



This species compares perhaps best with Cytherideis trigonalls Jones, 

 but is readily distinguished by its smaller size, more elongate form, more 

 obtuse cardinal angles, and coarser markings. 



The specific name is derived from that of Mr. George Asherman, of 

 Cincinnati, Ohio, who has for years spent much time in the collection of 

 these minute Crustacea and to whom we are indebted for disinterested 

 aid in the laborious task of picking specimens from our washings. 



Length of a very large and unusually elongate right valve 0.91 mm., 

 greatest height of same 0.44 mm., corresponding dimensions of a small 

 right valve 0.62 mm. and 0.31 mm., length of a rather large left valve 

 0.80 mm., greatest height of same 0.41 mm., thickness of a complete cara- 

 pace, having a length of 0.85 mm., about 0.3 mm. 



Occurrence. — Calvert Formation. Plum Point. Also in the Ches- 

 apeake Group at Yorktown, Virginia. 



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



Cytherideis cylindrica n. sp. 

 Plate XXXVII, Fig. 17. 

 Description. — Carapace very frail, elongate, cylindrical, with rounded 

 and nearly equal ends ; ventral outline straight, dorsal very gently arcu- 

 ate. A narrow marginal rim on the ends. Surface finely reticulate. 



