380 Systematic Paleontology 



slightly subcarinate along the median line near the beak. Beak sharply 

 pointed, closely incurved over that of the opposite valve. Brachial valve 

 a little less convex than the pedicle, its greatest elevation near the middle. 

 Surface of each valve marked by from fifty to sixty simple, rounded plica- 

 tions, which become obsolete before reaching the beak. 



" The dimensions of an average specimen are : Length 18 mm. ; width 

 16 mm.; thickness 11.5 mm." Weller, 1903. 



This species occurs typically and in abundance in the " Trilobite bed " 

 at Port Jervis in southern New York and was at first regarded by the 

 writer as a small form of R. cequiradiaia Conrad. The latter, however, is 

 much larger, about twice the size, proportionately more elongate, while 

 R. subglobosa in addition tends to vary into broad forms, and is more 

 abundantly striate. It is this Port Jervis form that is found in Maryland. 

 Here, however, another variation appears, tending to have fewer striae, 

 which in some specimens are rather plications, strongly elevated and 

 angular. 



The elongate common and more typical specimens greatly resemble 

 R. mutabilis, but are larger and far more abundantly striate. 



Occurrence.— Helderberg Formation, Becraft Member. Ernstville, 

 Maryland ; Cherrj' Eun, West Virginia ; Warren Point, Pennsylvania. 



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



EENSSELiERIA SUBGLOBOSA VAE. AVUS n. var. 



Plate LXVI, Fig. 13 



Description. — This variety differs from R. subglobosa in its broad sub- 

 circular form. In the Upper Oriskany it has become fixed into a distinct 

 species which attains a larger size and is here named R. circularis. 



Length 2.2 cm.; width 2.4 cm. 



Occurrence. — Helderberg Formation, Becjuft Member. Ernstville, 

 Maryland; Cherry Eun, West Virginia; Warren Point, Pennsylvania. 



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



