220 PALEONTOLOGY OF NEW YORK. ' 



from the Black River limestone of the Ottawa river ; a very similar shell is 

 the C. Panderi, described at the same time from the same locality ; indeed, there 

 may be reason to doubt if there is a valid specific difference in these shells, as 

 both the Canadian specimens and examples from the Trenton limestone of New 

 York (Jacksonburg), afford a series passing from the typical plicated form of one 

 to the non-plicated form of the other. 



Camarella Volborthi has full, convex valves, which are smooth about the um- 

 bonal region, but anteriorly develop a few low plications which are rather the 

 more conspicuous on the median fold and sinus, and the fold, sinus and plica- 

 tions are clearly developed on the often abrupt anterior slope of the valves. 



The pedicle-valve is the more convex up to maturity, but thereafter the 

 brachial valve becomes the deeper. The beak of the pedicle-valve is erect or 

 slightly incurved and beneath it lies a triangular delthyrium which, so far as 

 observed, shows, neither in this species nor in C. Panderi, any evidence of del- 

 tidial plates. The cardinal slopes are abrupt and oblique, and no cardinal area 

 is developed on either valve. On the interior are dental lamellse which con- 

 verge, and uniting, are supported by a short median septum, forming thus a 

 well-defined spondylium like that of Syntrophia. 



In the brachial valve the hinge-structure is similar to that of Camarotcechia, 

 the crural plates converging and forming a short, very small median cavity, 

 which is supported by a long septum. The crura are short and the lateral 

 divisions of the hinge-plate small. No cardinal process exists. 



The internal structure of Camarella is, thus, not unlike that of Syntrophia, 

 notwithstanding the Avide difference of exterior. 



Many American species have been referred to this genus, but, from present 

 knowledge it would seem to be quite restricted in range and specific representa- 

 tion. Apparently it does not pass beyond the faunas of the Lower Silurian, 

 and it is probable that most of the species referred to the genus by Mr. Billings 

 will prove to have been accurately placed, though in regard to some of them, 

 their rarity and unfavorable preservation make it impossible to be positive. 

 The species Camarella ? antiquata, Billings, from the early primordial faunas, may 

 or may not belong here ; we know it only from the figures of the exterior 



