CONTRIBUTIONS TO PALEONTOLOGY. 285 



characters of Strophalosia except the hinge-teeth and sockets, and 

 the disposition of the reniform impressions; while the New York species, 

 possessing teeth and sockets, have not the disposition of the reniform 

 vascular impressions which are given by European authors as character- 

 istic of Strophalosia. 



In glancing at the species of Productidse illustrated on Plates 23, 24, 

 25 and 26 of Vol. iv, Palceontology of New York, one cannot fail to be 

 imjDressed with the prevailing greater width on the hinge-line, and con- 

 sequent modification of form in the American Devonian species, as 

 compared with the Strophalosia of the Permian system in Europe. But 

 while the greater part, and perhaps all of these, have a narrow cardinal 

 area and small hinge-teeth and sockets, I conceive that their exterior 

 character and expression are much more like the true Productus than 

 are the Permian species of Strophalosia ; and one of the most marked 

 features consists in the conspicuous ears with rows of spines, as in Car- 

 boniferous Product!; while their anterior extension and highly arcuate 

 forms assimilate them much more with Productus than with Stro- 

 phalosia. 



The Productidas of this character make their first appearance in the 

 American geological series in the Upper Helderberg group, and continue 

 with increasing numbers through the successive formations to the Car- 

 boniferous limestone. There are a few individuals of two species in the 

 Corniferous limestone, and more in numbers of individuals and of other 

 species in the Hamilton group ; but it is difficult to find specimens in a 

 condition favorable for satisfactory investigation. A few specimens have 

 been obtained entirely separated from the rock; but nearly all are 

 imbedded, with the ventral valve adhering to the matrix so that the 

 hinge and interior structure can rarely be seen ; while the dorsal valves 

 almost uniformly adhere by their exterior surface, leaving only their 

 interior for examination. 



In the Chemung group, the specimens occur mostly as casts of the 

 interior and impressions of the exterior, and these are frequently much 

 distorted. In some of the softer compact shales of this group, we find 

 the shell partially preserved, but still in such condition that the entire 

 characters cannot be discovered ; and it is only in some fresh exposures of 

 the semicalcareous bands that we are able rarely to obtain specimens 

 of more natural appearance and better preserved surface. Under cir- 

 cumstances of so much difficulty, it is with much hesitation that I 



