CHAP. V. GENERA OF THE COLUMBELLIN^E. 



151 



characters of the ColumbelliniB in the highest perfection. 

 The three aberrant genera are more diversified. Thus, 

 Conidea (fig. 17. 6) has the general form of a short fusi- 

 form mitre (like Mitra contracta*), or that of a cone 

 with the spire as long, or longer, than the body -whorl, 

 but still with the volutions thickened at the suture, and 

 the aperture narrow : there are a few tooth-like striae on 

 the inner part of the outer lip ; but it is not thickened 

 in the middle : the inner lip forms an elevated ridge at 

 the base ; parallel to which is a longitudinal elevated 



fold slightly crenated ; but the tuberculated teeth on the 

 pillar are entirely wanting. In some species the spire is 

 rather lengthened, with the aperture widened : and this 

 change brings us to the 4th genus, Nitidella (c), where 

 the inner lip and its fold totally disappear ; the upper 

 part of the pillar, or rather that side of the whorl which 

 forms the aperture, is flattened, as if pared down arti- 

 ficially (as in Purpura) ; the base is finely striated, as 

 in Ancillaria, and is terminated by a distinct plait 

 (sometimes two), such as is seen in Folutilithes. All 

 these resemblances point to one type of structure, and 

 intimate this to be the most aberrant sub-genus of the 

 Columbellina. There are many species, but all small ; 

 the most common of which is the Colutnbella nitida of 

 Lamarck t, a little West Indian shell, in almost every 

 collection : the outer lip is either smooth or slightly 

 striated within; but although the edge is slightly 

 thickened, it is never contracted in the middle nor 

 is the margin, although inclining inwards, decidedly 



* Zool. in. 1st Series. 



f Nitidella marmorata. Sw. (fig. 17. c.) 

 T, 4 



