48« PALiEONTOLOGY OF NEW-YORK. 



there is sometimes no depression on the middle of the valve, and some- 

 times a strong angular sinus. Some separated valves of specimens from 

 Maryland show an arching transverse septum below the rostral cavity, 

 rising from the inner surface of the shell and leaving a deep pit beneath. 

 The casts present an appearance somewhat as if there had been a double 

 rostral cavity, one below the other. Although the internal structure is but 

 partially determined, I can have no hesitation in separating it from the 

 more abundant forms which I have recognized as Merista ; and I have 

 proposed for these fossils the generic designation of Camaeiom. 



Gems Camarilm ( n. g.). 



[ 6r. KOfiapa, fornix ; in reference to the arching septum.] 



Terebratula and yltrypa, in part, of authors. 



Merista, in part : Davidson, Hall, and other authors. 



Camarium : IIall, 1858. 



Shells ovoid or elliptical, and sometimes depressed subglobose : valves 

 articulating by teeth and sockets ; beak of ventral valve perforate. In- 

 terior of ventral valve marked by an arching transverse septum about 

 one-third the distance from beak to base. The inner surface of the shell, 

 above and below the septum, marked by muscular imprints : structure 

 of the crura, etc. of the dorsal valve unknown. Ventral valve ventricose, 

 flat or sinuate in the middle, and produced in a sublinguiform extension 

 in front. 



Surface marked by fine concentric stria) ; and partially exfoliated speci- 

 mens show some obscure radiating striaB. 



From the similarity of structure, I have presumed these forms to belong to the 

 same group as Spirigera and Merista ; but the presence of the transverse septum 

 seems incompatible with the existence of the internal spires which characterize 

 those genera. 



Under this genus I Include Merista princeps and M. meeki ( Pal. N.Y. Vol. iii 

 pp. 251 & 252, excluding figures 1-3, which may be regarded as doubtful ). I have 

 not yet been able to determine the internal structure, so far as to make satisfactory 

 comparisons with similar part* of Camarophoria. 



