354 Systematic Paleontology 



CAMAKOTffiCHIA GIGAXTEA 11. Sp. 



Plate LXIII, Pigs. 15, IG 



De^criiition. — Shell siibtri angular in outline. Width greater than the 

 length. Pedicle valve convex, greatest convexity in the umbonal region, 

 anterior to this somewhat depressed convex, beak closely incurved over 

 that of the dorsal valve. Sinus shallow and undefined posteriorly, be- 

 coming deeper and with more definite limits towards the front. Dorsal 

 valve larger than the ventral valve, extremely gibbous, greatest convexity 

 two-thirds the distance from the beak to the anterior, sloping gradually to 

 the beak and abruptly to the anterior and lateral margins. No well-de- 

 veloped mesial fold; beak strongly incurved under that of the ventral 

 valve. Surface marked by simple, well-defined, round, radiating plications, 

 which are more elevated and prominent towards ihe anterior and though 

 not becoming obsolete they are not so prominent in the umbonal region. 

 About 18 to 20 plications on each valve, five of -which may occupy the 

 sinus on the ventral valve. The dorsal margins are abruptly deflected 

 posteriorly and become rounded towards the front. 



This form resembles most closely Camarotcechia siricklandi (Sowerby) 

 of the Niagara. It is of about the same size, but differs in having the 

 plications of equal size upon the sides and in the mesial sinus. Sinus nar- 

 rower, no prominent mesial fold. The reference of this species to the 

 genus Camarotcechia is not assured as the interior of the shell has not been 

 observed. 



Length about 2.5 cm. ; width about 3 cm. 



Occurrence. — Helderbekg Foumatiox, Keyser Member, Devil's 

 Backbone, Cash Valley. 



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



[Maynard.] 



Subgenus PLETHORHYNCHA Hall and Clarke 



Camarotcechia (Plethoriiyncha) campbellana (Hall) 

 Plate LXIII, Figs. 17-19 



Kynchonella campbellana Hall, 1857, Tenth Ann. Rept. N. Y. State Cab. Nat. 

 Hist., p. 79. 



