the Lingual Dentition in the Gasteropoda. 239 
in mingling it with Bucc’num.” The buccinoid type of ribbon 
is nevertheless invariably found with Nassa, Cyclonassa, Pusio- 
stoma (Sw.), Myristica, and numerous other genera strictly ap- 
pertaining to the family. But if Ricinula, Planaxis, Cassis, 
Columbella, and Oliva are placed in the same category, the 
dental characters will assuredly be found wanting; for the 
genera just mentioned cannot, with any justice to zoological 
science, be distributed into less than five distinct families apart 
from Buccinide. 
I conclude therefore that, until all the families of the Gas- 
teropoda have been sifted in this way, superfluous families re- 
jected and nature’s own families found, we cannot be in a 
position to affirm that the dental characters are not in all cases 
to be depended upon—though this may be in reality quite 
true. 
If it is intended, by the assertion that the “ teeth are essen- 
tially epithelian cells,” to lessen their morphological importance 
and convey the idea of mutability, surely we ought to be able 
to draw a distinction between the normal and abnormal deve- 
lopment of the same organs in different members of the same 
species. Moreover the teeth are formed from a special matrix 
at the fundus of the lingual sac, determining in every case the 
constant evolution of certain characters ; and any defect in the 
formative pulp will repeat any consequent malformation in 
each succeeding row of teeth. 
If it is implied that, as it were, obedient to circumstances 
affecting adaptation, nature may possibly give a buccinoid 
ribbon to a veritable Murex, such a doctrine is quite untenable. 
My own impression is that the distinctive characters of the 
teeth are in accordance with a definite plan, whether we asso- 
ciate this with the adaptation of the creatures to the special 
conditions of their existence or not. Any one finding Helicina 
(a truly terrestrial Nerite) and Helix (an inoperculate bisexual 
snail, with a broad lingual pavement) feeding in a tropical 
forest under precisely similar circumstances, would be inclined 
to yield the palm to the plan rather than to the conditions of 
existence. On Mr. Darwin’s beautiful hypothesis, the diver- 
gence of species from a primitive type may be readily admitted; 
yet, like the coloured components of white light diverging 
from the prism, it would be unphilosophical to suppose them 
capable of reciprocally interchanging their characters and 
properties, even if it were possible to refer all to a common 
source. 
No one would approve of establishing the peculiarities of the 
dentition of Mammalia or of any other great class of animals 
as a kind of ready reckoner of affinities, without taking into 
Lia, wes 
