CLASSIFICATION. 67 



between a natural classification of the shells and one founded 011 

 dentition, according to Prof. Morch, will disappear. " I have 

 united in the family Tritonidse, according to the sculpture, 

 Ranella, Triton, Pyrula (Ficus), Dolium, Cassidaria and Cassis, 

 placing them near to C3 r praea." This is in accord with the 

 character of their dentition, which widely removes Triton and 

 Ranella from the Muricidse, close to which they have heretofore 

 been placed, upon conchological characters principally the form 

 of the shell, the presence of varices, the operculum, and also 

 upon a decided resemblance of the animals. 



I have carefully re-examined these genera and their relation- 

 ships with others, in the point of view taken by Prof. Morch, and 

 the result of this examination is to convince me that he has in 

 the first place selected in the sculpture a character that is of 

 generic importance only in the single genus Dolium that is to 

 say, its species happen to possess revolving ribs, and that even in 

 the sculpture the relationship of Triton and Ranella with Murex 

 is exceedingly close, whilst they have little or no affinity with 

 Dolium, Cassis, etc. In fact, it is precisely because Prof. Morch 

 has regarded lingual dentition a priori as an " infallible cri- 

 teriuni"that he has been enabled to detect supporting resem- 

 blances in the shells. It is easy to show in many other instances, 

 as in the group under discussion, how heterogeneous is the 

 assemblage united by means of the " infallible criterium." There 

 is, besides, a growing conviction, in which I share, that there are 

 no sharps-defined groups in nature ; that a generic character, for 

 example, cannot be made to cover all its species; that upon its 

 borders occur forms which partake of the characters of other so- 

 called genera, and that families, orders, etc., similarly coalesce 

 upon their confines. I anticipate a future period when our larger 

 collections, together with our better knowledge of external influ- 

 ences and of the power of adaptation to them of these creatures, 

 shall reveal to us a series of recent and fossil forms having rela- 

 tionships 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 affinities. The value of a classification 

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



