144 SHELLS AND SHELL-FISH. PART I. 



(133.) Our next comparison will be between the 

 types of form in the genus Pterocera, and the genera 

 of the StromhincB. 



Analogy of the Types of Form in the Genus Pterocera. 



Types of Analogies. Genera of 



Pterocera. 



Analogies. Strombin^. 



Lambis. Basal canal greatly lengthened. Pterocera. 



Millipeda. Basal canal short. Strombhs. 



_. _, COuter lip thickened, and inflected 7 «TDni»iiTnn'A 



Sinuata. [ inwards ; basal canal truncate, j ^trombidea. 



T ^- • f Outer lip extending to the apex 7 -p n^rrr,, , .-oj . 



LaUsmnus. \ of the spire, and Intire. ' j Rostell^ria. 



r Canal resembling the digitated'^ 

 Chiragra. < processes of the lip, and turned 5- Aporrhais. 



L on one side. 3 



In such small groups as these, we cannot expect the 

 analogies to be very strong; a faint resemblance is all 

 that exists — and all, indeed, that is necessary. Yet it is 

 remarkable how perfectly P. latissimus corresponds to 

 the RosteUaria macroptera in its excessively large outer 

 lip, which, in both shells, runs up to the top, and even 

 spreads far beyond the apex of the spire. 



(134.) The analogies of the genus Stromhus are nume- 

 rous, and, in some measure, too complicated to be here 

 introduced : it will be sufficient to remark, that, besides 

 the five leading divisions or types of form, there may be 

 discerned indications of another set of secondary types ; 

 so, that, if such groups were better understood (as no 

 doubt they will be hereafter), some of them may be 

 found to contain representations of the primary genera 

 of the StromUncp, no less than of its leading divisions. 

 The time, however, is not yet come for such an elaborate 

 .study of analogies as this implies ; and we shall, there- 

 fore, merely place before our readers the five divisions 

 of the genus, which, as already specified, seem to be 

 represented by the five following shells: — Stromhus 

 Auris.BiantE, gigas, lentiginosus, gibberulus, and suc- 

 cinctus. All these are among the most common species, 



