280 NOTES ON THE PERMIAN SYSTEM OF 



Two of the original casts of Bissoa obtusa, Brown, are not in 

 a state good enough to describe. One of tliem is very much 

 compressed. The other specimen is more perfect than these, 

 hut is also a cast. It has four rounded whorls and a short 

 spire, but the apex is not quite perfect. The Natica minima, 

 Brown, a cast Avith imperfect spire, is undoubtedly the same as 

 R. obtusa. The originals of Capt. Brown's Eissoa Gihsoni are 

 also casts. Two of them are ver}^ much compressed, so that 

 the spire has not the natural appearance. The third specimen 

 closely resembles the R. obtusa, but its spire is longer, being 

 more perfect than the others at the apex. 



The estuarine character of these Lancashire shells was pointed 

 out, many years ago, by Mr. Binney, in the " Manchester Geo- 

 logical Transactions," vol. i., and this opinion was very forcibly 

 impressed upon me when examining the originals belonging to 

 that gentleman. The larger and more typical individuals from 

 the shell-limestone of Durham have probably lived in less con- 

 fined habitats, but still they have a decidedly littoral character. 

 It must be mentioned here that I have used the term " littoral " 

 in contradistinction to " pelagic," and not in the limited sense in 

 Avliich it is used by British naturalists. 



This species occurs in the middle and up23er divisions of the 

 magnesian limestone, but the most typical and finest specimens 

 are from the shell-limestone of Tunstall. 



2. L. Hercynica, Geinitz. 



Dr. Geinitz had described and figured this species in the 

 " Versteinerungen," several months before Mr. King's imper- 

 fect notice of it in the " Cat. Org. Eem." appeared. It was 

 identified in the " Tyneside Catalogue " Avith Natica minima, 

 Brown ; but an examination of the latter proves this identification 

 to be incorrect. Dr. Geinitz and Mr. King both place this shell 

 in the genus Natica, but it is rather difficult to comprehend why 

 they do so, for it has a nearly orbicular mouth, is not apparently 

 a polished shell, is not umbilicated, and bears a strong resem- 

 blance to the Littorince. By comparing the mouth of this 

 species (Perm. Mon. pi. IG, f. 28) with that of L. hvlicina Cpl. 



