130 



SHELLS AND SHELL-FISH. 



We shall make no other commentary upon this table, 

 than as regards the rank of the groups in each column, 

 which are thus shown to be genera. The sub-genera 

 of the Volutince, it will be remembered, we have indi- 

 cated, but not named, because the species they contain 

 are so few, and these so well known, that it might be 

 thought a needless multiplication of names. But in the 

 present family the case is widely different : as not one 

 third of the mitres are figured, and the descriptions of 

 most of the remainder are too vague to admit of deter- 

 mination, it becomes absolutely necessary, not only to 

 characterise, but to name, the sub-genera. This we have 

 accordingly done, — confining ourselves, however, to the 

 two typical genera, which, as in all such groups, con- 

 tain the great majority of the species. The foregoing 

 table shows that Mitra and Tiara are the two groups 

 in question; and, as the definitions of their sub-genera 

 will be hereafter detailed, we shall at once lay before 

 the reader the exposition of their analogies. 



Analogies of the Genera Mitra and Tiara. 



Sub-genera of 



Mitra. 



Internal canal 



wanting; aper- 



ture smooth. 



Mitra. 



Tiarella. 

 Scabricola. 

 Nebularia. 

 Strigatella. 



rSpii 



\ I 



Analogical Characters. 



re and aperture of equallength, " 

 nequally fusiform ; body- \ 

 whorl obtuse. 



Sub-genera of 



Tfiiara. 

 With an internal 

 canal ; aperture 



striated. 



Costellaria. 



f Shell with distinctly coronated, 7 

 \ acute, or obtuse tubercles. J 

 C Shell with numerous elevatedribs, ^ 

 •< longitudinal in one, transverse > 

 L in the other. j 



(" Shell reticulated or cancellated ; 7 

 i the base of the aperture effuse. J 

 Size very small ; outer lip thick- '^ 

 ened, and generally gibbous > 

 ithin. S 



f Size 



Tiara. 



Callithea. 



Cancilla. 



Pusia. 



It thus appears that each of the divisions, or sub- 

 genera, of Mitra finds its representative in Tiara; and 

 that, without a due regard to the essential characters 

 which distinguish these two genera, it will be impossible 



