Maryland Geological Survey 439 



slightly more prominent than the others ; and, between these, there is a 

 third smaller depressed plication, forming an indistinct sinus. On the 

 dorsal valve the two middle plications are a little closer together, and 

 slightly more prominent near the front, than the others; while the de- 

 pressions separating them from these, each side, are a little wider and 

 deeper than those between the other plications." Hall, 1859. 



This well-known and prolific species has a very extended geographic 

 distribution in both hemispheres, especially in eastern North America 

 and at many places in Bolivia, Brazil, the Falkland Islands, and in 

 South Africa. Its geologic distribution is also extensive. Near Cherry 

 Run, West Virginia, the writer collected two small examples in the New 

 Scotland zone and two medium-sized specimens in the Becraft. In no 

 way, other than in size, are these distinguishable. In the Lower Oriskany 

 of western Maryland, at many localities, this species is the commonest 

 fossil, and it occurs throughout not only this division but the Upper Oris- 

 kany as well. From the latter horizon come the best specimens and often 

 in considerable numbers. 



Length 1.6 cm.; width 1.8 cm. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Cherry Run, West Virginia. Becraft Member. Oriskany Formation, 

 Shriver Member. Common. Ridgely Member. Common. 



Collections. — Maryland Geological Survey, U. S. National ]\Iuseum, 

 American Museum of Natural History. 



Family MERISTELLIDAE 



Genus WHITFIELDELLA Hall and Clarke 



Whitfieldella ( ?) prosseri Grabau 

 Plate LXXIII, Figs. 34-3G 



Meristella Icevis Whitfield, 1891, Ann. N. Y. Acad. Sci., vol. v, p. 510, pi. v, 



figs. 6 and 7. 

 Meristella kvvis Whitfield, 1895, Ohio Pal., vol. vii, p. 411, pi. i, figs. 6 and 7. 

 Meristella Iwvis Sherzer, 1900, Geol. Survey Mich., vol. vii, p. 223, pi. xvii, 



figs. 6 and 7. 

 Whitfieldella cf. lavis Grabau, 1900, Bull. Geol. Soc. Amer., vol. xi, p. 369, 



pi. xxil, figs. ia-d. 

 Whitfieldella prosseri Grabau, 1910, Michigan Geol. Surv., Publication 2, 



Geological Ser. 1, p. 152, pi. xxi, figs. 3, 8, 9, 12-13; pi. xxx, figs. 6-7. 



