42 [Assembly 



OBSERYATIONS ON TIE GENUS CAMAEIUM. 



Among the fossil species referred by me to the Genus Merista, and 

 published in the Heport of the Regents of the University in 1856 

 and 1857, and printed in the Palseontology of New- York, vol. iii, 

 in the latter year, are several which, although possessing the general 

 external form of Merista, present nevertheless some noticeable pe- 

 culiarities. One of these is, the strongly incurved beak of the ventral 

 valve, while the cardinal margin is abruptly bent inwards, leaving 

 an angular or subangular ridge extending from the beak to the 

 margin of the shell, the space between this and the cardinal margin 

 being sometimes flattened about halfway to the base. The front of 

 the shell is often produced in a broad linguiform extension of the 

 ventral valve : there is sometimes no depression on the middle of 

 the valve, and sometimes 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 de- 

 signation of Camarium. 



Genus Camarium ( n. g.). 



[ G-r. xaixaQa, for^iix, in reference to the avcliing septum.] 



Terelratula and Mrypa, in part, of authors. 



Merista, in part : Davidson, Hall, 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. Interior of ventral valve marked by an arching trans- 

 verse 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. 



