226 



SHELLS AND SHELL- FISH. 



PART I. 



Analogies of the Sub-genera oyTRocHus and Monodonta. 



Sub-gencra of 

 Trochus. 



Trochus. 

 TrochUicm. 



Calliostoma. 



Pagodella. 



Chlorostoma. 



] 



Analogical Characters. 



More or less umbilicated, but the 

 umbilicus always smooth. 



Base of tlie pillar forming a pro- 1 

 minent tootii. J 



Imperforate, smooth, or slightly "J 

 granulated ; basal whorl some- { 

 times ventricose ; spire long, f 

 pointed. j 



Shell not perlaceous, pyramidical. 



Deeply umbilicated; the inner ^ 

 lip thickened and truncate > 

 half way round the margin, j 



Sub-genera of 



Mo.NODOiV. 



Monodonta. 

 Fragella. 



Elenchus. 



Echinella. 

 Monilea. 



These analogical resemblances are so close, that, but 

 for the former explanations, an incautious conchologist 

 might easily mistake one for the other. Unfortunately, 

 we are in total ignorance of the animals of all these, 

 Trochus excepted. Whether they have each a peculiar 

 modification of form, or whether Nature has confined 

 herself to tracing out these variations by the shells 

 alone, are questions which time alone will develope. 



(211.) "A natural arrangement," as an eminent en- 

 tomologist has more than once observed, "^ will stand any 

 test." We have now placed it in the reader's power to 

 act upon this hint, by applying all those " tests " which 

 our preceding diagrams have supplied, to our arrange- 

 ment of this family. There is one, however, which, 

 from its singularity, may here be mentioned. 



Analogies of the Tbochid^ to the AcHAxiNiE, 



Sub- families of 



TllOCllIU/E. 



Senectin-e. 



Trochin*. 



kotellin.e. 



Pleurotomin^. 



FilASIANELLIN£. 



Analogical Characters. 



("Ventricose ; sjiire short ; aperture \ 

 X always entire. J 



C Spire conic, inore developed ; base \ 

 X of the pillar notched or toothed. 3 

 Nearly discoid. 



r Outer lip, either above or below,7 

 X with a slit. j 



Spire very much produced. 



Genera of the 



ACH.\T1N^. 



Bllimls. 



achatina. 



Cyclostoma. 



Helicina. 



CLAL'SILIA. 



