368 Systematic Paleontology 



the dorsal valve. It has in some individuals more plications and the 

 plications are more angular than in Uncinulus nucleolatus. In the an- 

 terior portion the sinus and fold when present are less distinct and the fold 

 is not prolonged anteriorly to form the linguiform extension seen in 

 Uncinulvs nucleolatus. 



Occurrence. — Helderbeeg Formation, Keyser Member. Cash 

 Valley. 



Collection. — U. S. National Museum. 



[Maynard.] 



Uncinulus keyserensis n. sp. 

 Plate LXV, Figs. 7, 8 



Description. — Associated with the Lower Coeymans form of U. nucleo- 

 latus are other individuals in greater abundance, distinguished by fewer 

 plications, all of which are decidedly angular and never depressed and 

 rounded as in that species. U. keyserensis usually has four plications on 

 the fold, but there may be an additional one, while the sinus has either 

 three or four. The number of plications on a valve varies in different 

 individuals between twelve and seventeen, while the associated specimens 

 of U. nucleolatus have from eighteen to twenty. As in U. nucleolatus, 

 this species also has the sharp linear depression along the center of the 

 lateral plications near their anterior terminations. This Uncinulus char- 

 acter, however, has a tendency to be less, developed and even lost in the 

 angularly plicated U. heyserensis. The specimen illustrated is one of 

 average size, but individuals nearly twice as large occur rarely. 



Length 14 mm. ; width 15 mm. 



OccMrren.ce.^HELDERBERG Formation, Keyser Member. Miller's 

 Spring and Mullen's Quarry, Cumberland, Dawson, Tonoloway, Mary- 

 land ; Keyser, West Virginia. 



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



Uncinulus convexorus n. sp. . 

 Plate LXV, Figs. 9-14 

 Description. — Shell trigonal or somewhat pentagonal, width at least 

 two-thirds the length. Ventral valve convex, abruptly deflected in front. 



