*^'  trenton limestone. 221 



Genus CAMEROCERAS (Conrad). 



Character. " Straight ; siphuncle marginal ; a longitudinal septum, forming a roll or 

 involution with the margin of the siphuncle." 



The above description is quoted from Mr. Conrad ( Jour. Acad. Jfat. Sci. Philadelphia, 

 1842, Vol, viii, p. 267 ) ; and although dissenting from his opinion of the characters in 

 part, I have adopted it as a distinct genus, closely allied to Endoceras. There is no 

 evidence of a longitudinal septum as described above, in the specimens I have examined ; 

 nor is it probable that such a character exists. The character of the siphuncle, though 

 resembling that of Endoceras, is different from any examined. 



286. 1. CAMEROCERAS TRENTONENSE. 



Pl. LVI. Figs. 4a,b,e. 

 Cameroeerat trentonensis. Conrad, Jour. Acad. Nat. Sci. Philadelphia, Vol. viii, pag. 287, pi. 16, fig. 3. 



Elongated, gradually tapering ; section elliptical, with diameters about as five to seven, 

 slightly contracted at intervals ; septa distant about one third the longest diameter of the 

 tube ; siphuncle marginal, contracted between the septa, obliquely annulated at the junction 

 of the septa. 



The single species differs from the Endoceras in its oval form, which is slightly con- 

 tracted at intervals. The siphuncle is marginal, occupying one of the extremities of the 

 ellipse, which is unequal at the two ends. The siphuncle is not only marked with the septa, 

 but is contracted between them, in some slight degree, like Ormoceras. The oval form and 

 contraction of the shell is constant and uniform in four specimens examined ; and the same 

 is true of the one described by Mr. Conrad, on which account we may presume it to be the 

 original form of the shell. 



This is a rare species, and the only one of the genus known. 



Fig. 4 a. A fragment of the shell, preserviog about three of the chambers, beyond which the siphon is 



extended to an equal distance. 

 Fig. 4 b. Another fragment, with the siphuncle still more extended. 

 Fig. 4 c. Transverse section, showing the position of the' siphuncle. 



Positi&n and locality. This species occurs in the higher part of the Trenton limestone, 

 associated with the other species of the same family, at Middle ville. («'«'« Collection.) 



