ro PALEONTOLOGY OF NEW-YORK. 



Notwithetanding tliose slight differences, I feel disposed to recognize the 

 two as distinct; though, adopting the line of argument which has been used in 

 regard to the Lower and Upper Helderberg Strophodontaj*, I should be compelled 

 to regard the S. pandora as identical with S. woolworthana. There will be found, 

 moreover, among the species of several genera of the Brachiopoda from the Lower 

 and Upper Helderberg formations, a like degree of similarity as I have already 

 flhown to exist between the Niagara and the Lower Helderberg species. 



The conditions prevailing during the epoch of the Upper Helderberg formation 

 wore very similar to those during the Lower Helderberg, the two being separated 

 by the Oriskany sandstone and Cauda-galli grit. There was, during the older period, 

 a greater amount of shaly matter deposited than during the later period, which is 

 almost wholly calcareous, and we have in the entire fauna an adaptation to these 

 conditions. 



The 8, pandora first appears in the Schoharie grit, where it occurs in considerable numbers, 

 although generally in the condition of casts. It has, in this part of the formation, attained a 

 diameter of nearly two inches in some of the larger specimens. Figs. 11 - 19 of Plate iv 

 represent its usual condition in this rock. Fig. 12 is drawn from a cast of a ventral valve, 

 made in a natural mould in the stone. Figs. 11, 15 & 16 ar oasts of the dorsal valve, while 

 13 & 18 are casts of the ventral valve. Fig. 14 is an artificial mould of the interior, from a 

 cast in stone, and docs not fully represent the cardinal process. Fig. 19 represents a specimen 

 with the sides more regularly carved than usual. 



The figures on Plate ix, from 18 to 25 inclusive, are of specimens from the Corniferous 

 limestone ; showing the dorsal, ventral, and profile views of a symmetrical specimen, with the 

 interior of the two valves, hinge-line, etc. 



The figs. 19 - 23 of Plate x are illustrations of the casts of symmetrical forms from the 

 Chemung group, and which difiier in no essential degree from the S. pandora of the Corni- 

 ferous limestone. 



The casts from the Schoharie grit show stronger muscular impressions, owing to the thicker 

 ■hell ; while the Chemung forms, having lived among sediments containing little calcareous 

 matter, have had a thinner shell, and consequently the muscular imprints arc less conspicuous 

 in the cast. 



Geological formation and locality. In the Schoharie grit at Schoharie, Knox- 

 villo, Clarksville and other places, and in the Corniferous limestone at Clarksville 

 and Schoharie; at Eastman's quarry south of Utica ; in Ontario county, and at 

 Clarence-hollow and Williamsvillo in Western New- York ; and in Canada West ; 

 being coextensive with the Limestone formation in this State and Canada. 



* BiujHos in Canadian Journal, Jaly, 1861. 



