SPIRXFERiE OF THE CHEMUNG GROUP. 
S45 
The interior of the ventral valve shows the presence of more or less 
extended dental lamellae : these are sometimes short and divergent, 
enclosing a pretty broad muscular space, and often less divergent and 
reaching nearly to the front of the shell; and the muscular imprint is 
sometimes pushed very far forward, and enclosed in a narrow space. 
The muscular markings are often well defined in the casts, but in some 
of them the markings of the ribs are shown over the muscular space. 
The fissure is closed for one-third or more of its length from the apex by 
a thickened plate or septum, with the rostral cavity more or less ex¬ 
tended behind it. In casts of the dorsal valve, we have the imprints of 
the cardinal muscles and the cavities made by the bases of the crura. 
This species has been recognized by European authors as Spirifera 
disjuncta, and identical with S. verneuili, etc., as shown in the synonymy. 
From comparison of ours with European specimens of that species in my 
own collection, I can find no important distinction; indeed the differences 
in a few indviduals are not as great as those among our own specimens 
recognized as belonging to the same species. It is regarded in Europe as 
a very characteristic Middle and Upper Devonian species; but in the 
State of New-York, it is not known out of the Chemung group. 
The Spirifera whitneyi is from beds of the age of the Hamilton group 
in Iowa, and bears a very close resemblance to the S. archiaci as figured 
in the Geology of Russia (ut cit). Some specimens of this form more 
recently examined^ show a variation in aspect and general characters 
which induce the conclusion that this one also is only a variety of S. 
disjuncta, occurring at a lower horizon in the west than yet known in 
New York; thus giving it a vertical range equal to the Middle and Upper 
Devonian of Europe. 
I have heretoforef given some of the varieties of this species under 
distinctive names, which have been abandoned after the study of larger 
collections. I have also been able to satisfy myself with regard to the 
* Specimens received from Mr. 0. St. John, of Waterloo, Iowa, 
t Geological Report of the Fourth District of New-York, pp. 270, 271. 
