872 THE PALEONTOLOGY OF MINNESOTA. 



[.Protowarthia cancellata. 



PROTOWARTHIA CANCELLATA Hall. 



PLATE LXIII. FIGS. 1-14. 



Belterophon cancellatus HALL, 1847, Pal. N. Y., vol. i, p. 307. 



Compare Beltei-ophon bilobatus of Hall and other American authors, not of Sowerby. 



The general form of this shell is much as in P. rectangularis and P. planodorsata, 

 the average of characters being about intermediate between these two species. 

 From the first it is distinguished by the more rounded back of the volutions and the 

 rounded instead of angular outline of the apertural lobes. The sinus in the outer 

 lip also is less V-shaped. From the second it is sufficiently distinguished by the 

 rounded instead of broadly flattened dorsal region of the last whorl. Young speci- 

 mens, especially if casts only were compared, would perhaps prove inseparable. 



We refer here a large number of casts from the Black River and Trenton groups 

 of Minnesota and elsewhere, as well as casts and testiferous specimens from the 

 Utica, Loraine and Richmond groups of the Cincinnati region. The specimens from 

 the Trenton period might be separated as var. trentonensis, as they are almost 

 constantly a trifle more narrowly rounded dorsally than is the geologically higher 

 typical form of the species. And yet we have specimens from the Black River 

 group at Chatfield, Minnesota, that are, so far as it is possible to determine, precisely 

 the same as the common variety of the species found in the lower part of the strata 

 at Cincinnati, and which we regard as typical of the species. 



Specimens preserving the shell in a satisfactory manner are everywhere rare. 

 The outer layer which carries the transverse and revolving lines is nearly always 

 gone, and, so far as our observation is concerned, this layer is retained, if we except 

 two or three instances, only by specimens that have been removed from the solid 

 limestone. These show that the perfect shell was ornamented with fine lines of 

 growth, generally a little unequal, and even finer (just visible to the naked eye) 

 revolving lines. The former may be obscurely visible on the inner layers of the 

 test, but the latter are entirely superficial. Now, while most of the testiferous 

 examples are almost entirely smooth, the greater number preserve the irregular or 

 wavy revolving lines which surround the umbilical regions. This is true not only 

 of this species but of the preceding forms as well, and proves that these thin exten- 

 sions of the callosity of the inner lip are composed of a more durable substance 

 than is the usual sculpture-bearing layer of the shell. So far as observed the inner 

 whorls are not granulose dorsally as is the case in P. granistriata, P. pervolufa and 

 P. planodorsala. The umbilical callosities of the inner lip are shai-ply defined, 

 oblique and somewhat flattened, though always more or less excavated. 



We have not seen the original type of this species which Hall sought to separate 

 from the specimens which he regarded as Bell, bilobatus. But we have little or no 



