PYRAMIDELLID A. 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 Chemnitzie 
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 
Chemnitzie. 
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 mstance, 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 
