V2 



and the author of MiiK-ral Conchology has incorrrctly placed it among' 

 the Cerithia, and he has been unfortunate in selecting a specimen for 

 representation, which on account of the state of the anterior part of the 

 columella, has the appearance of justifying this view of it. This is, 

 therefore, the shell that is most perfectly identified by Defrance as his 

 Melania inquinata, though it is also extremely probable that he has not 

 distinguished from it other shells which are found in France. In re- 

 lation, however, to the above-mentioned circumstance, which Defrance 

 considers very singular, namely, that the tubercles are often broken 

 and replaced by small cavities, I must not omit to state, that it can only 

 be regarded as a proof that the shells were inhabitants of the fresh or 

 brackish waters of rivers, lakes, or estuaries ; that the tubercles are not 

 actually broken, but eroded in the same manner as the points and other 

 prominent parts of MeJaniae, NcriliniE, and other fresh water and 

 estuary shells commonly are, such erosion being continued, until in 

 place of tubercles a small cavity has been formed. These little cavities 

 then that replace the tubercles are not to be regarded as a character of 

 the species ; and the first result of the examination, as far as I have 

 hitherto gone, is that the shell named by Sowerby in Mineral Con- 

 chology Cerithium melanioides is the Melania inquinata of Defrance. 

 I find, that in the Index to Mineral Conchology it is referred to under 

 the name " Potamides politus (melanioides)" by which I understand 

 J. D. C. Sowerby to express his opinion, that this is one of those shells 

 that may with propriety be separated from the Cerithia under Brong- 

 niart's generic term " Potamides" (in French), or " Potamis" (in Latin) : 

 the opinion thus expressed isjikhowever, not compatible with fiict, for 

 the shell is a true Melania. 



I must next enquire how far the fossil shells given by Desliayes under 

 that name, agree with the true Melania inquinata of Defrance. And to 

 put my readers in possession of the whole subject with the least pos- 

 sible trouble to them, I sliall copy, vk^ord for word, what Deshayes has 

 said upon it, in his Description des Coquilles fossiles des environs de 

 Paris. 



