PYKAMIDELLID.E. 407 







lating a button- shaped point, which may be, and is, often 

 mistaken for that of a Rissoa by the incautious observer, 

 leaving a greater or less portion of the other part of the coil 

 soldered to the second volution and microscopic aid is often 

 required to detect these divisions of the terminal inflexions ; 

 but to the really observant and experienced malacologist, 

 there is a certain aspect and peculiar twist at the antepenulti 

 mate bend of the inversion, which detects the true concho- 

 logical Chemnitzian character. The only species we know of, 

 in which any difficulty can arise by the subreflexion or bend 

 on the second volution exhibiting a more subdued character 

 of the apex, by being sunken or deposited in a groove or 

 depression, with a more graduated arcuation, are the Chem- 

 nitzia pallida, C. spiralis, C. nivosa, Mont., and the R. dia- 

 phana of Mr. Alder his Jeff, 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 Chemnitzia 

 have their terminations unmistakeably inverted. We have 

 examined and described all the animals, except that of 

 C. nivosa, of the less inflexed species, and they are all decided 

 Chemnitzice. 



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 

 genus, and others of all its species with intensely continuous 

 apertural margins not mere testaceous deposits which only 

 simulate the continuity of the peristome ; but as a general rule, 

 the periphery of the aperture is more usually discontinuous ; 

 nevertheless the exceptions are numerous. 



As to the characters of the umbilici, they are most falla- 

 cious ; for instance, in the Chemnitzia pallida, and, in fact, in 

 every species, there are individuals with every variation of the 

 umbilicus, from the open and patulous to the mere fissure, 

 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 particular individual. The fold or 

 tooth, except its presence or non-presence, as a character, as 

 we have stated above, is equally fallacious ; for in the same 



