Mr C. Collier on Univalves. 235 



understood, in every system of natural history, that distinctions' 

 are drawn from the perfected individuals. 



This arrangement breaks up, if the expression be allowed, 

 the Linnaean Bulla ; but a slight acquaintance with conchology 

 will shew that this affords no solid objection, considering that 

 very dissimilar shells are comprised under it. 



3. The difference between Conus and Valuta is but in de- 

 gree, and not so essential as to constitute a generic separation. 

 The inner windings of the pillar of the former are as cylindri- 

 cally rolled or voluted as those of the latter, and the bases in 

 some individuals of both are alike, or nearly so *. If these be 

 united by an adjective to the feature of assimilation (Columno- 

 volutum) the genera repose upon the minor distinctions of 



Jiirrowed or plain condition of that feature. 



4. Those shells which are furnished with a rostrum or heak, 

 seem classed in nature, and may be expressed by the term 

 rostratum. The direction of this feature constitutes the divi- 

 sions. This arrangement is proposed partially by M. Cuvier 

 in his fifth table, but so mixed up with spiriform shells, and 

 so connected with the consideration of the animals, that it does 

 not interfere with this system. 



5. The spiral T^rjTz, being a permanent feature, constitutes 

 the essential character of, and therefore unites many univalves. 

 This, adopted as significant of a family, embraces Trochis^ 

 Turbo, Helix, Nerita. 



These shells present great difficulties, it is true, in the at- 

 tempt at more perfect arrangement and nomenclature, and they 

 shew the impossibility of equalizing, in an artificial system, the 

 profusion and individuality of nature. The generic feature 

 seems to belong to all, and thus to constitute them a. family ; 

 but the minor qualities are not so apparent, nor so capable of 

 discrimination. The turbinated shape, which is assumed in an 

 ordinary acceptation by Trockus and Turbo, being, after the 

 spiral, the more general characteristic, is ajirst division. The 

 existence of two lips, or the double margin (formed by the 

 edge of the columella), which is now the diagnosis of Nerita 



" The spires and apices are also similar in respect to their variety in 

 botli ; the former sometimes exserted or retusc, the lalter acute or papUlanj. 



