1847.| SHARPE ON THE PALHOZOIC ROCKS OF N. AMERICA. 161 
shall find some groups of shells common in the United States long 
before we meet them here. 
In the genus Spirifer some of the sections may be pretty evenly 
matched in the two continents, while others appear at different 
epochs. The following are in the former case :— 
In the section of Biforés of De Verneuil, we find in the Lower 
Silurian beds 
S. biforatus, var. Lynx, Chama, &c., in the United States. 
S. dentatus, Pander, 
S. terebratuliformis, M‘Coy (erucialis >in England. 
of Sedgwick’s list), 
Among the species with fine striee, either alone or im addition to 
strong rays, the following are found in the Middle and Upper Silurian 
beds of the two countries :— 
S. radiatus, : ; S. radiatus, saad 
S. Niagarensis, hs saosin S. interlineatus, in England. 
S. macropleura, ; 
And many large-winged, expanded species are found in both countries 
in the Devonian formation. 
But there are several large species of Spz7zfer found in the United 
States in the equivalents of the Wenlock formation, or in the beds 
next above them, of forms which we are only accustomed to see here 
in the carboniferous series. Such are the following :— 
S. arenosus, a shell so like the usual carboniferous species, that 
M. de Verneuil doubted the correctness of the localities marked 
on specimens sent him from Bogoslofsk with Silurian and 
Devonian species (‘ Russie,’ vol. 1. p. 164), where the species is 
named S. superbus. 
S. undulatus, of Hall, not of Sowerby. 
S. (unnamed), a large strongly-marked species nearly allied to S. 
erassus, but with a smooth mesial fold. 
In the Upper Pentamerus limestone, a bed belonging to the Wen- 
lock series, there occurs a small spinose species of Productus allied 
to P. laxispina, P. Cancrini, &c. ; such as we only find in Europe in 
the Devonian and carboniferous formations. 
These instances ought to teach us that all classifications of the 
formations of distant countries are very liable to error when they are 
only based upon the generic resemblances of the organic remains. 
Had a bed been found containing only the species just mentioned, it 
would, in the absence of other evidence, have been referred by com- 
mon consent to the carboniferous system: whereas a preponderance 
of evidence derived from the identification of species forces us to class 
these in the Wenlock series. Even when we have one or two iden- 
tical species to rely upon, we may be easily mistaken in our estimate 
- of the age of a foreign formation: but a classification is of very little 
value which only rests on finding, in two distant places, shells of the 
same genus or section of a genus ; or upon what have been called re- 
presentative species. 
VOL. IV.—PART I. oO 
