386 Systematic Paleontology 



radial striae and shell obesity, while a side and less prolific branch tends 

 to retain the juvenile characters of a nearly smooth and lentiform shell, 

 but adds a well-defined false area and sharp but neat inflection of the 

 valve margin — Beachia. The interior characters in tlie terminal forms 

 are somewhat different, but in the early species they probably are alike. 



Length about 10 mm. ; width about same. 



Occurrence. — Heldeebeeg Formation, Keyser Member (upper part) . 

 Pinto, Maryland; JSTew Bloomfield, Pennsylvania. 



Collection. — U. S. National Museum. 



Renssel.eria (Beachia) cumberlandi^e (Hall) 

 Plate LXVII, Figs. 4-6 



Meganteris cumberlandice Hall, 1S57, Tenth Ann. Rept. N. Y. State Cab. Nat. 



Hist, p. 101. 

 Rensselaria cumherlandiw Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 464, 



pi. cvlii, figs, la-1/, 1861. 

 Rensselaria cuml)erlandi(C Hall and Clarke, ihidem, vol. viii, pt. ii, p. 258, pi. 



Ixxvii, figs. 23-25. 



Description. — " Shell oval, ovate or elliptical ; valves nearly equal, some- 

 what acutely rounded in front ; no trace of a sinus in either valve ; lateral 

 margins abruptly inflected : ventral valve rounded and most convex along 

 the middle, sloping laterally and forming a broad semielliptical curve 

 from front to beak, a little more gibbous above than below the center; beak 

 prominent, slightly arched ; extremity perforate ; i:)erf oration generally 

 connected with the broad triangular foramen below, but probably often 

 separated by the deltidial pieces, which, with the thickened dental 

 apophysis, nearly or quite close the foramen: dorsal valve depressed 

 convex, slightly the smaller; beak scarcely incurved. Surface apparently 

 smooth, or marked only by obscure concentric lines and faint wrinkles of 

 growth." Hall, 1857. 



This species is most closely related to R. cvquiradiata and R. suhglohosa 

 of the Becraft and Shriver members. It is, however, readily distinguished 

 by the nearly or complete obsolescence of the radial plications, the presence 

 of concentric growth rugosities, and the angular inflection of the lateral 

 and anterior edges of the valves. 



