916 CLASS III. GASTEROPODA. ORDER VII. PECTINIBRANCHIATA. 
COLUMBELLA, Lamarck. 
Testa parva, ovato-oblonga, vel trigona, interdum subfusiformis, ad 
basem emarginata; apertura coarctata, angusta ; columella arcuata, 
denticulata, rard levi; labro externo incrassato, mediané tumido 
aut gibboso, seepissimé denticulato. Operculum minutissimum, cor- 
neum. sd 
This genus is one which Lamarck proposed in the plenitude of his en- 
thusiasm, without sufficiently considering the nature of the characters upon 
which he founded it. The columellar denticulations which characterize the 
shells of the Columbellz were incautiously regarded by that naturalist as 
plaits, as if they were analogous to, or rather a modification of, the plaits of 
the Mitre or Volute ; the difference first noted by De Férussac may, how- 
ever, be easily detected on examination. In the Mitre, &c., the plaits are 
strongly developed in all stages of growth, winding round the entire pillar 
of the shell through every whorl ; the plait-like denticulations of the Co- 
lumbellz, on the contrary, are not formed until the shell arrives at ma- 
turity ; they are exhibited, therefore, only in adult specimens, and are 
precisely analogous to the plait-like denticulations of the Ricinule. This 
will readily account for our arranging this genus with the Purpurifera in 
imitation of De Férussac, Gray, and Quoy, instead of with the Columel- 
lata in conformity with Lamarck ; it may be also proper to notice, that 
the few of Lamarck’s Columbelle, which are actually plaited, belong pro- 
perly to the genus Mitra. 
The shell of Columbella may be described as being small, ovately- 
oblong, or triangular, occasionally somewhat fusiform, and always emar- 
ginated at the base ; the aperture is contracted, and narrow ; the columella 
is curved, and denticulated, though sometimes, but rarely, smooth; the 
outer lip is thickened, always swollen or gibbous towards the middle, and 
generally denticulated. The operculum is horny and very small. 
