CLASSIFICATION. 69 



It is not partial, but pervades nearly the whole mollusca as well 

 those which have no lingual ribbon ; its universality is the proof 

 of its higher systematic importance ; its relationships are not 

 single, it is the epitome of the modifications of molluscan struc- 

 ture. Supposing the dentition of all living forms to be examined 

 (an impossibility), we are still confronted by the fossil shells, 

 which absolutely refuse to be classified by any other than con. 

 chological characters. What shall we do with them ? Shall we 

 use for these 30,000 species obvious external, universal charac- 

 ters, yet discard these in the recent mollusca for the modifications 

 of a partial character, the very slight observation of wliich has 

 sufficed to show that it may not be predicated with certainty 

 from either the shell, operculum, external features, or anatomy of 

 the animal ? 



Whilst I shall continue to find in the shell the usual characters 

 for the discrimination of genera and families, I shall not refuse 

 all the aid which I can obtain from the study of lingual dentition 

 as well as from all other sources which may enable me to more 

 rightly appreciate natural relationships, to correct error, to avoid 

 it. For the present, I prefer to treat Triton and Ranella as 

 transitional genera having many relationships with the Murices, 

 but partaking in their dentition and in some other structural 

 details in the characters of ( -assis, Polium, etc. 



Prof. Theodore Gill published in 1871, under the auspices of 

 the Smithsonian Institution an " Arrangement of the families of 

 Mollusks." largely founded on their lingual dentition. Whilst 

 this classification presents many features as novel as praiseworthy, 

 reflecting the highest credit on the philosophical views and 

 critical acumen of its author, it is, I think, equally unacceptable 

 with those classifications heretofore proposed by European 

 authors in which this character has been used as an exclusive 

 guide. I reproduce Prof. Grill's arrangement below, as far as it 

 relates to the Rhachiglossate mollusca. It will be noticed, as 

 particularly affecting the groups of mollusks included in the 

 present and succeeding volumes of this Manual, that the families 

 of Fasciolamdffi (including Fusinre) Buccinidae,and Muricidse arq 

 widely separated, being each placed under a group founded on a 

 modification of dentition, and that other families of mollusks 

 otherwise not nearly related to these, are nevertheless interposed 



