CLASSIFICATION. 261 



similarly coalesce upon their contines. We may anticipate a 

 period when our larger collections, together with oar better 

 knowledge of external influences and of the power of adaptation 

 to them of these creatures, shall reveal to us a series of recent 

 and fossil forms having relationships so intimate, that our present 

 system of classification and resulting nomenclature shall become 

 utterly valueless. 



In this point of view classification is essentially arbitrary and 

 we can only help ourselves by choosing that which does least 

 violence to natural aflfinities. The value of a classification 

 foimded on a single organ (the lingual ribbon), which does 

 violence to other apparent affinities, whilst at the same time it 

 fails of signification even in one of the most important functions 

 with which it is connected, in that it does not enable us to 

 certainly separate the phytophagous from the zoophagous animals, 

 may be seriously questioned. We have many most important 

 characters of the mollusks which impress themselves upon their 

 shells, so that they are in accord and enable us to predicate 

 reciprocally their relationships ; and such characters appear to 

 rae to be much more useful for classification. 



Mr. Wm. G. Binney, who has devoted a number of years to 

 the study of the dentition and anatomy of terrestrial mollusks, 

 has recently given the following guarded opinion upon the value 

 of the jaw and lingual membrane for the purpose of classification. 



" It is conceded by all recent students of land shells that for 

 the larger divisions the presence or absence of a jaw and the 

 aculeate or quadrate form of marginal teeth are reliable characters. 



" The characters of the jaw and separate teeth of the lingual 

 membrane have also been used in various ways for grouping the 

 genera into families, etc., and even of grouping species into 

 genera. I refrain from any discussion 'of their value for such 

 purposes, simply because I believe our material is far too limited. 

 It seems as if I can better employ my time in patiently accumu- 

 lating new facts. I can, however, venture to say that the 

 character of the jaw and teeth seems to be more constant in 

 some genera than in others. It appears, for instance, that in 

 some genei'a the presence or absence of lateral teeth is not a 

 generic character, though in others it is. The same may be said 

 of the presence or absence of side-cutting points to the centrals 

 and laterals, and the greater or less development of their side 

 cusps ; also in the bifurcation or non-bifurcation of the cutting- 

 point of aculeate marginal teeth ; also as to the presence or 

 absence of ribs on the jaw. 



" It will, 1 believe, be proved that certain genera are constantl}^ 

 characterized by a peculiar form of teeth, while others have a 

 considerable range of variation. I might, perhaps, add that 

 when the genus is numerous in species, there is a much greater 



