MARYLAND GEOLOGICAL SURVEY 101 



Description. — The valves of this species are oblong and obscurely 

 trapesoidal in outline, with the dorsal and ventral margins subparallel, 

 the former straight or very gently concave, the latter straight or very 

 slightly convex, the ends subequal but converging dorsally so that the 

 ventral half is longer than the dorsal half. Eim of valves distinct, 

 double on the anterior end and narrow, growing almost obsolete about 

 the middle of the ventral edge and wider again in the postventrai 

 region, near which also the surface has its greatest convexity. In the 

 posterodorsal angle there is a well defined submarginal node, and just 

 in front of the center of the valves a less distinctly defined small swell- 

 ing. Excepting the marginal rims, which are smooth, the entire sur- 

 face is covered with subangular pits, which occasionally present an 

 irregular concentric arrangement. No marginal spines have been 

 observed. 



Length of a left valve 0.86 mm., height of same O.-IG mm., thickness 

 of same 0.32 mm. 



It is difficult to decide from the few left valves before us whether 

 the relations of this species are nearer C. angulatopora (Reuss) Bosquet' 

 or C. nystiana Bosquet. In having no marginal spines it corresponds 

 with the latter and differs from the former, but when this feature is left 

 out of consideration the relations are reversed. In most respects our 

 species occupies an intermediate position between the two European 

 OsTRACODA with which Ave have compared it, yet as it seems to possess 

 a few characters not shared by either of them it has been deemed advisable 

 to refer to the x\merican form provisionally luider a new name. 



Occwrence.— Calvert Formation. Plum Point. 



Collections.— [] . S. National Museum, Maryland Geological Survey. 



Cytiiere in^quivalvis n. sp. 



Plate XXXV, Figs. 15-17. 



Description. — Carapace elongate, the outline approaching that of a 

 parallelogram, very insequivalved, 1.1 mm. to 1.2 mm. in length, 0.5 mm. 



1 According to Jones and Sherborn the C. avgiilatopora of Bosquet is not the same 

 species to which Reuss applied that name. They have therefore proposed the new 

 name C. bosquetiana for Bosquet's species. 



