114 SYSTEMATIC PALEONTOLOGY 



secured it seemed a better plan to regard the two as representing a dis- 

 tinct though closely related species. Perhaps it is worth while to add 

 that C. dorsicornis is a trifle smaller than average specimens of C. 

 martini. 



Length of a left valve 0.68 mm., height of anterior end 0.39 mm., 

 height of posterior end 0.27 mm. 



Occurrence. — Calvert Formation. Plum Point. 



Collection. — U. S. National Museum. 



Cythere dorsicornis var. bicornis n. var. 

 Plate XXXVIII, Figs. 32, 33. 



Description. — This variety differs from the typical form of the species 

 (1) in having two instead of a single spine, the second one being situ- 

 ated near the opposite border of the valve; (2) in having fewer surface 

 pits, these being restricted to the central part of the valve and mostly 

 to the posterior half; (3) in having two low and inconspicuous swellings 

 on the depressed portion of the dorsal slope between the dorsal spine 

 and the anterocardinal node; and (4) in being smaller. 



Length 0.47 mm., greatest height 0.28 mm. 



This form and, in a smaller degree, the typical variety of the species, 

 as well, exhibits certain features that are more strongly developed in 

 C. haccata, Jones and Sherborn, from the Pliocene of England. Our 

 species probably is more intimately related to this English species than 

 appears at first sight, but their specific distinctness is too obvious to be 

 questioned. 



Occurrence. — Choptank Formation. Pawpaw Point. 



Collection. — U. S. National Museum. 



Cythere lienenklausi n. sp. 

 Plate XXXVIII, Pig. 31. 

 Description. — This very pretty and on the whole well marked species 

 seems to be more closely related to our C. martini than to any other 

 known to us. It occurs associated with that species at Plum Point, 

 but is a much less common and even smaller fossil. The left valve, 

 which is usually a little higher than the other in species of this type. 



