232 SHELLS AND SHELL-FISH. PART I. 



typical form in Stomatia imhricata and sulcifera, which 

 appear to have from two to three distinct spiral whorls *, 

 but Still without any ridges or angles, although the 

 outer surface is finely imbricated. In duplicata the 

 spire is still more developed, angulated, and marked 

 with granulated tubercles; so that, in fact, it much 

 more resembles one of the SenectincB, and particularly 

 Cidaris, than a Stomatia, while its angulated shape and 

 tubercles remind us of Delphinula. Lastly, v/e have a 

 form, in S. phimotis, very distinct from all these : the 

 spire is again shorter, more like that of planulata and 

 auricula, but it is irregularly formed; the outside of the 

 shell is rough and angulated, as in duplicata, so that it 

 unites the form of all these three ; we have an indis- 

 tinct recollection, also, that the substance of this shell is 

 not pcrlaceous, like all the preceding species. Now, the 

 reader, if he turns to our distribution of the Trochidce, 

 and of the types therein contained, cannot fail to be 

 struck with the singular coincidence of these five spe- 

 cies agreeing with the variations there pointed out. 

 This will be seen more clearly by throwing them into 

 a tabular form. 



Analogies of the Types of Stomatia. 



Types of ^ , „ Trochid^. 



Stomatia. Analogies. ,^,yp^^_ 



V ^7^^..?^,^ f Spire flattened: outer surface 7 Rotella, 



!>. piamtlata. ^ smooth. j Cidaris. 



vhimoth or C Shell and spire irregular; subo 



?SSaLm.] stance not perlaceous; outer f Onustus. 



C. surface rough, cannated. J 



^iiT.u;'^^^ r Spire elevated ; the whorls angu- 7 Delphinula, 



aupucata. ^ lated and coronated. j Canthoibis. 



,» . • » f Spire short, raised above the body- 7 q„„^ ,. „ 



Auricula. ) \^^^^ . ^erlaceous. j Senectus. 



rSpiremore elevated and developed, ^ 



^ but witliout any angles or tu- > Trochus. 



L bercles. 3 



imbricata. 



We are unacquainted with any of the fossil species, 

 but we have no doubt, after this exposition, that they 



* Sowerby's Genera, art. Stomatia, figs. 1 and 2. 



