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 

 Pterocera. 



Lambis. 

 MilHpeda. 



Sinuata. 

 Latissimus. 



Chimsra. 



Analogies. 



Basal canal greatly lengthened. 



Basal canal short. 

 f Outer lip thickened, and inflected 7 

 (_ inwards ; basal canal truncate. J 



f Outer !ip extending to the apex > 

 X of the spire, and entire. J 



1 



Canal resembling the digitated 'J 

 processes of the lip, and turned > 

 on one side. j 



Genera of 

 Strombin.e. 



Pterocera. 

 Strombus. 



Strombidea. 



RosTELLiVRIA. 



Aporriiais. 



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. latisslmns 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 Stromhns 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 cf them may be 

 found to contain representations of the primary genera 

 of the St7'otiibin(e, 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: — Sfromh7<s 

 Atiris-Dkinrp, yiyas, lentig'mosus, gihhernhis, and suc- 

 cinvius. All these are among the most common species. 



