Marylaxd Geological Survey 381 



Renssel.^iua subglobosa var. crassa n. var. 

 Plate LXVI, Fig. 14 



Description. — This variety is a coarsely striate or plicate form of E. 

 subglohosa. It has from 25 to 4() plications on each valve, while the 

 parent type has from 50 to 65 striae. 



Length 2.3 cm. ; v/idth 1.8 cm. 



Occurrence. — Heldeeberg Formation, Becraft Member. Warren 

 Point, Pennsylvania. 



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



EENSSEL.aiRIA CIRCULAKIS n. sp. 



Plate LXVI, Figs. 15-17 



Description. — This species is the fixed tapper Oriskany form of the 

 Lower Oriskany R. subglohosa var. avus, and it seems to be the stock that 

 gives rise to R. cayuga Hall and Clarke. It is readily distinguished from 

 other Oriskany Rensselserias by the nearly circular outline. The dorsal 

 valve is regularly depressed convex and the ventral valve is deeper and 

 somewhat ridged down the center. The lateral margins are not inflected. 



R. circularis differs from R. cayuga and R. ovulum Hall and Clarke ^ 

 in being from two to three times smaller and more circular in outline. 

 Some of the young specimens of R. cayuga, if found alone, would be re- 

 garded as R. circularis, and this fact shows that the former is probably 

 a descendant of the latter ?pecies. 



Long after this description was written the writer received Clarke's work 

 " Some New Devonic Fossils " ^ in which is described R. atlantica. The 

 new form is from the Chapman Plantation, Maine, and is very similar to 

 the Maryland species. The former is smaller, more rounded, with a less 

 incurved ventral beak. 



Length 3.5 cm.; width 2.7 cm. 



^ The writer has a large series of these species from the typical locality, and 

 they grade into each other so completely that but one name can he applied to 

 them. K. cayuga will be retained. 



" Bull. 107, N. Y. State Mus., 1907, p. 243. 



