MARYLAND GEOLOGICAL SURVEY 139 



Occurrence. — Choptank Formation. On Peach Blossom Creek, 3 

 miles southwest of Easton. Calvert Formation. Plum Point and 

 Church Hill. 



Collection. — U. S. National Museum. 



Genus CYTHEROPTERON G. O. Sars. 



Cytheropteron nodosum n. sp. 

 Plate XXXVIII, Figs. 37-40. 



Description.— Oi this remarkable species a single right valve only has 

 been observed. It is strongly but very irregularly convex, with a low 

 and broad swelling in the anterior half, another large protuberance in 

 the postcardinal fourth, a third smaller node just within the depressed 

 and somewhat produced posterior extremity, and a fourth, wing-like 

 prominence, that attains a greater altitude than the other nodes, on the 

 posterior end of a well-defined ventral ridge. In addition to these there 

 is a small spine near the posteroventral angle and a small knob just 

 within the anterodorsal angle. The outline is elongate, subtrapezoidal, 

 the ends subequal, with the anterior slightly the wider, obliquely trun- 

 cate, converging dorsally. The ventral outline is gently convex and 

 slightly overhung by the posterior third of the ventral ridge. The dorsal 

 outline is slightly concave, the concavity being due chiefly to the pro- 

 jection of the postcardinal node. The central part of the surface is 

 depressed, forming a broad though not sharply defined sulcus. A sharply 

 outlined, bevelled border encloses the ends, the posterior border continu- 

 ing forward to about the middle of the ventral edge where the bevel is 

 reversed and turned inward to form the small concave area that is more 

 or less readily distinguishable on the majority of the Ostracoda of this 

 family. The anterior border does not meet the border coming from the 

 opposite end but passes on above it as an impressed line which gradually 

 becomes obsolete a short distance behind the middle of the ventral side. 

 The surface ornament consists of somewhat scattered pits of moderate 

 size. 



Length of a right valve 0.68 mm., height of both ends each about 0.30 

 mm., greatest thickness about 0.25 mm. 



The rudely nodose or hummocky surface of the valves of this species 

 9 



