Mr. W. Clark on the Chemnitzise. 385 



subdued character of the apex, by being sunken or deposited in a 

 groove or depression, with a more graduated arcuation, are the 

 Chemnitzia paUida, C. spiralis, C. nivosa, Mont., and the R. dia- 

 phana of Mr. Alder, our Chem. diaphana — not the C. diaphana of 

 some authors, which is the young of C obliqua, and perhaps there 

 may be one or two more ; all the remaining Chemnitzim have their 

 terminations unmistakeably inverted. We have examined and 

 described iu the memoir above referred to all the animals, ex- 

 cept that of C. nivosa, of the less inflexed species, and they are 

 all decided Chemnitzia. 



With regard to the continuity and interruption of the peri- 

 stome in Chemnitzia, I can say that neither character is to be 

 depended on. I have in my cabinet elongated shells of this ge- 

 nus, and others of all its species with intensely continuous aper- 

 tural margins,, not mere testaceous deposits, which only simulate 

 the continuity of the peristome ; but as a general rule, the peri- 

 phery of the aperture is more usually discontinuous ; nevertheless 

 the exceptions are numerous. 



As to the characters of the umbilici, they are most fallacious ; 

 for instance, in the Chemnitzia pallida, and iu fact in every spe- 

 cies, there are individuals with every variation of the umbilicus, 

 from the open and patulous to the mere jSssure, and from it to 

 the entirely imperforate one. To use the umbilicus at all is most 

 deceptive ; it can only be mentioned in the description of a par- 

 ticular individual. The fold or tooth, except its presence or non- 

 presence as a character, as we have stated above, is equally fal- 

 lacious ; for in the same species it is often strong, slender, small, 

 prominent and retired. Such characters cannot fail to mislead 

 and confuse the young student. 



The first and best characters of a Chemnitzia are undoubtedly 

 the malacological ones we have given above, when they can be 

 had ; the next are of conchological value, the inflected apices, 

 which however will almost always shadow out what the animal 

 of a shell will prove ; and the tooth, however minute and rudi- 

 mental, is an excellent aid ; and we may add, the flap or process 

 of the operculum. All others from their instability lead to error 

 and confusion ; but if they are brought forward as specialties, it 

 should be sub modo, with explanatory guards and limits, and in- 

 dications of their variableness. 



I now approach the catalogue raisonne, and will amalgamate 

 with it the additions and new matter under the titles to which 

 they belong. Perhaps it may be conceded that a sedulous exa- 

 mination of these interesting objects for more than forty years, 

 has in some measure placed me in a position to offer a reformed 

 list of the British Chemnitziee, which will include all the animals, 



Ann. ^ Mag. N. Hist. Ser. 3. Fo/. vii. 25 



