238 Dr. J. D. Macdonald on the Typical Value of 
“The patterns or types of lingual dentition are on the whole 
remarkably constant, but their systematic value is not uniform. 
It must be remembered that the teeth are essentially epithelian 
cells, and, like: other superficial organs, liable to be modified 
in accordance with the wants and habits of the creatures. The 
instruments with which animals obtain their food are of all 
others the most subject to those adaptive changes, and can 
never form the basis of a philosophical system.” And I add 
here a note from the bottom of page 450 :—‘‘ The carnivorous 
opossums have teeth adapted for eating flesh, but are not on 
that account to be classed with placental carnivora.” 
To state that the systematic value of the types of lingual 
dentition is not uniform implies, first, that we are fully ac- 
quainted with a subject which is yet avowedly only in its in- 
fancy ; and, secondly, that from this knowledge notable in- 
stances may be advanced demonstrating the truth of the asser- 
tion. We are surely not to form a hasty conclusion to this 
effect from the analysis of such a family as the Bullide, for 
example, including a mass of beings differing as much inter se 
as the families of Pteropoda, and much more than the three 
acknowledged families of Heteropoda do. Now the principle 
which I desire to maintain is that Gasteropoda whose general 
anatomical characters, including the configuration, sculp- 
turing, and minute structure of their shells, suggest their 
distribution in the same group will be found still further to 
be associated as well as distinguished by the type and pecu- 
liarity of their lingual dentition—moreover, that prima facie 
resemblance or difference, with or without conformity in the 
dentition of the animals, may only require a little further 
investigation to reveal their natural affinities or antipathies. 
Anticipating myself a little, I think I may sately state, from 
extended observation, that Concholepas, Purpura, Ricinula, 
Vitularia, or any other genus properly referable to the Mu- 
ricide will always be found with a lingual dentition unequi- 
vocally on the type of that of Murex. But if some Pisanie, 
Ranella, Triton, Fasciolaria, and other equally incongruous 
genera are associated with them, it is no wonder that the den- 
tition should be found to exhibit no “uniform systematic 
value.” For further illustration we may select the Buccinide, 
whose dental characters are so distinctive that any single 
genus properly belonging to it can never be confounded with 
Muricide or any other family. The excellent authorities 
Forbes and Hanley (vol. i. p. 888), speaking of the genus 
Nassa, remark that ‘it is one of the best marked and most 
easily recognized groups, both as to shell and animal, among 
the Muricide (!), though some conchologists strangely persist 
