ATRYPA OF THE CHEMUNG GROUP 325' 



Figures 1-7, are from the Upper Helderberg limestone. 



Figures 8-14, present the ordinary forms and phases of the species in the Hamilton group ; figures 8 

 and 9, retain the spines, and the others have them removed. 



Figure 14, is of the interior of a well marked ventral valve. 



Figure 18, presents the ordinary phase of this species in the Chemung group. There are sometimes 

 remains of short spines, as shown in the accompanying woodcut. 



Figures 24 and 25, show the spiral cones of the interior viewed from the dorsal and ventral side re- 

 spectively. 



Geological formations and localities. — This species occurs in the Corniferous 

 limestone, in nearly all the localities cited for A. reticularis. In the Hamilton 

 group, its principal localities are Moscow and York in Livingston county, Darien 

 in Genesee county, Hamburgh and Eighteen-mile creek in Erie county ; likewise 

 on the shores of Seneca and Cayuga lakes, and eastward of these points. It occurs 

 in the same formation in Maryland and Virginia, in Canada West, and in Iowa 

 and Illinois. In the TuUy limestone, it is found at Tinker's falls, Onondaga coun- 

 ty, New York. In the Chemung group, it occurs in considerable numbers on Ca- 

 yuta creek at Factoryville ; at Chemung, Chemung creek and Chemung-narrows, 

 and at Bath and vicinity ; also at Elmira and northward of that place. It become* 

 rare or altogether unknown in the southwestern counties of this State. 



and the costae coarser than in the Hamilton and Chemung specimens of /I. reticularis ; but these dis- 

 tinctions cannot be fully illustrated till we know more intimately the structure and character of all its 

 parts. While these pages are going through the press, 1 have examined more than a hundred speci- 

 mens of this form and of the finely costate species, and find no difficulty in separating them one from 

 the other though there are remarkable variations in individuals. In making the comparisons and 

 references to Atrypa reticularis, I have adopted that name for the more finely costate forms, but I am 

 compelled to e.xpress some doubt whether we fully understand the original of that species. After much 

 careful study of the interiors of several genera of Brachiopoda, including Atrypa, I still hesitate to 

 accept the general opinion regarding a species which is so well known, and is found abundantly in all 

 the formations from the Devonian to nearly the bottom of the Silurian system, and which has received 

 the following appellations : 



jinomites reticularis, Wahlknbeeo, Nov. Act. Soc. Upsal, Vol. viii, p. 65. 



Terebratulites priscus, Scblotheim, Petrefact., PI. Ixxxvii, f. 9. 



Terebratula ajinit, Sowekbt, Miu. Conch. PI. cccxxiv, f. 2, etc., etc. 

 If this, in all its phases, be a single species, there are many of the species designated under other 

 genera of Brachiopoda, which hare no better claim to specific value, subject to the same rule. 



