166 PALAEONTOLOGY OF NEW-YORK. 



This species has been referred to Pterinea by Mr. Conrad, with the remark that it •' has 

 much resemblance to certain species of the Grenus Inoceramus." It is probably identical 

 with that described by Mr. Portlock ( cited above ) , who adds the remark, that Professor 

 Phillips regards it as belonging to the Genus Posidonia of Bronn. It is true that our shell 

 approaches to Posidonia in many respects ; but in other essential characters, it differs from 

 that genus. The species here grouped under a new generic name, may be regarded, 

 perhaps, as the representatives of a type, which, in a later geological period, appears in 

 the Posidonia ; but the species under consideration, and its congeners, cannot, I apprehend, 

 be properly placed under the Genus Posidonia. Strictly speaking, the present species has 

 few of the distinguishing characters of Inoceramus, except the broad undulations which 

 mark some species of that genus as well as of Posidonia. It cannot therefore be admitted 

 into that genus, and we are compelled to construct a new term, under which this and the 

 preceding ones may be arranged. 



Our species bears a close analogy with Inoceramus vetustus of Sowerby, from the 

 Carboniferous limestone ; but that one is more distinctly alated, both as represented by 

 Sowerby and by Goldfuss : neither can we, for a moment, believe that this species of the 

 older Silurian rocks, after such an immense lapse of time, should reappear in the Car- 

 boniferous strata, while we have scarcely an analogous form in all the intermediate strata. 

 If the geological position of Mr. Sowerby's specimen be correctly cited, it is not probable 

 that the one described by Capt. Portlock is identical ; for from its associates, as well as 

 precise similarity to our own, we regard it as of lower Silurian age. 



Fig. 7 a. Right valve of a specimen which is imperfect on the lower side. 

 Fig. 7 b. Profile of the stune, looking upon the posterior side. 



Position and locality. In the higher crystalline portions of the Trenton limestone, asso- 

 ciated with Edmondia suhtruncata, Suhulites elongata, and several of the common Brachio- 

 pods of the rock. Watertown, Jefferson county. {State ColUetum, from Dr. Cbawe.) 



