486 
PALAEONTOLOGY 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 Camarium. 
Genus Camarium (n. g.). 
[ Gr. napapa, fornix; in reference to the arching septum.] 
Terebratula and Atrypa, in part, of authors. 
Merista, in part : Davidson, IIall, and other authors. 
Camarium : Hall, 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 strise; and partially exfoliated speci¬ 
mens show some obscure radiating striae. 
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. meelci ( 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 parts of Camarophoria. 
