406 PYRAMIDELLIDJD. 



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 inhabited 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 Chemnitzia there are numerous phases 

 of inflexion, from the most decided to the more obtusely- 

 pointed 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- 



