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. 



Scdbricola. 



Nebularia. 



Strigatella. 



Analogical Characters. 



r Spire and aperture of equallength, } 

 -< unequally fusiform ; body- S- 

 C. whorl obtuse. J 



f Shell with distinctly coronated, 7 

 I acute, or obtuse tubercles. j 

 C Shell with numerous elevatedribs, } 



< longitudinal in one, transverse > 

 C in the other. .) 

 ("Shell reticulated or cancellated ; 7 

 I the base of the aperture effuse. J 

 f Size very small ; outer lip thick- 



< ened, and generally gibbous 

 t within. 



Sub-genera of 



Thiara. 



With an internal 

 canal ; aperture 



striated. 



Costellaria. 



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 



