406 PYRAMIDELLID A. 
vidual of this genus from every other. These characters, 
allowing for specialty-variations, are essentially the same, 
whether the animal inhabits a shell of two or twenty volu- 
tions, whether they be tumid, rounded, flat, smooth or plicated, 
or coiled on a discoidal plane. In this genus, with two excep- 
tions, we throw overboard form and markings, with respect 
to generic attributes, regarding all such points as only useful 
specialties. The first exception is the constant peculiarity in 
the form of the apex: this is never absent, though it is 
attended by numerous modifications of inversion, which, how- 
ever slight they may be, always prognosticate that a shell 
with this character is mhabited by a true Chemnitzia. The 
second exception is the tooth or fold on the columella, which, 
when present, however variable in figure and position, I have 
always found to be an unerring indication that the animal is 
of Chemnitzian type; but as it is often absent, even in the 
same species, we have only its occasional assistance. With 
these views, we cannot see the utility of a divisional arrange- 
ment of the group; we can only acknowledge the genus 
Chemnitzia in its comprehensive integrity for the animal we 
have defined. 
With respect to the apices, it is necessary to impress on the 
student, that in all the Chemnitzie there are numerous phases 
of inflexion, from the most decided to the more obtusely- 
poited or button-shaped subreflexions. The variations arise 
either from original configuration, or the forms become tra- 
vestied from the effects of attrition, which will reduce the 
most conspicuous inverted points, of even good fresh speci- 
mens, to a button-shaped, sunken, or subreflected apex. Mala- 
cologists may not be aware that live shells, especially the 
littoral ones, are more liable to suffer from the attrition 
caused by the tides and waves than those of the deeper zones ; 
and the true characters of their apices are with greater diffi- 
culty appreciated from being enveloped in calcareous and 
other extraneous deposits, the removal of which often destroys 
the true figure of the apex, and conchologists are thus misled. 
In many of the apices both of live and dead shells the coil is 
rubbed through, leaving a part which becomes worn, simu- 
