130 



SHELLS AND SHELL-FISH. 



PART I. 



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 he 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 

 wiU be hereafter detailed, we shall at once lay before 

 the reader the exposition of their analogies. 



Analogies of the Genera Mitra and Tiara. 



Sub- gen era of 



Mitra. 

 Internal canal 

 wanting ; aper- 

 ture smooth. 



Mitra. 



Tiarella. 

 Scabricola. 

 Nebularia. 

 Strigatella. 



Analogical Characters. 



Sub-genera of 



Thiara. 



With an internal 



canal ; aperture 



striated. 



f Spire and aperture of equallength, "i 



< unequally fusiform ; body- > 

 t whorl obtuse. j 



("Shell with distinctly coronated, 7 

 X acute, or obtuse tubercles. j 



f Shell with numerous elevated ribs, f 



< longitudinal in one, transverse V 

 C in the other. j 



("Shell reticulated or cancellated ; 7 



X the base of the aperture effuse. 3 



Size very small ; outer lip thick 



ened, and generally gibbous 



within. 



\ 



} 



Costellaria. 



Tiara. 



Calliihca. 



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 



