524 Systematic Palf-ontology 



Genus CTENOBOLBINA Ulrich 

 CtENOBOLBINA ? DENTICULA n. Sp. 



Plate XCVI, Figs. 6-9 



Description. — Carajiace elongate, siibovate, tapering anteriorly; hinge 

 long and straight ; surface gently convex, thickest anteriorly and sloping 

 somewhat abruptly toward this extremity, granulose, and in some speci- 

 mens with punctas between the granules; median sulcus moderately de- 

 veloped, slightly curved and dividing the shell along the median line; 

 immediately behind the sulcus a rounded node of considerable size, though 

 no great prominence, is observable ; the rest of the body of the valve rather 

 evenly convex. Occasionally a small spine in the posterior half of the 

 dorsal edge ; flange or frill narrow, but developed rather uniformly along 

 the entire length of the free edge of the valve ; edge of frill bearing a row 

 of small spines which are most conspicuous in the posterior edges. On the 

 anterior end the contact edge beneath the flange bears denticles. 



Length of right valve 1.45 mm. ; height .82 mm. 



One of the type specimens has a granulose surface, while the siirface of 

 the second, in addition to the granules, presents rather regularly placed 

 punctae. Whether the latter condition is a specific character or is due to 

 weathering cannot be determined from the material at hand. The position 

 of this specimen is somewhat questionable. If it really belongs to Cteno- 

 bolbina, then it must be classed with the suhcrassa section of the genus, 

 but the post-median node is longer than in any other known species of the 

 genus. The shape of valve, size, character and granulose marking of 

 flange and contact edges, is as in typical Ctenobolbina. Considering the 

 large size of the node, it is possible that the species is nearer Kloedenia, 

 but for reasons mentioned, also the absence of a sulcus behind the node, 

 this relation seems more questionable than the one given the species. 



Occurrence. — Helderberg Formation, Keyser Member. Cumber- 

 land. 



Collection. — U. S. National Museum. 



