154 



SHELLS AND SHELL-FISH. 



Analogies of the Strombid^ arid the Mitring. 



Families of the . , ■ , ^z. u Genera of the 



STROMBID.E. Analogical Characters. Mitring. 



Strombus. Shell generally rugged. Tiara. 



PlEu»oio„A. ["fi^fSfed"'"''"'""'""""] Con„,telu. 



Cerithium. ? Mitrella. 



(143.) Without going further into particulars, we 

 may observe that these tables afford strong collateral 

 evidence that the strombiform structure — at least, in this 

 order — is one of the primary types of form, which is 

 repeated and represented, under every possible modifi- 

 cation, in almost all the groups hitherto noticed. 



(144.) The Pleurotomin^ is our next sub- family. 

 The perfect gradation of forms which connects this 

 remarkable group with the cones, will, it is presumed, 

 remove all doubts as to its supposed affinity with the 

 FusincB. Nothing, indeed, short of the evidence here 

 adduced would have satisfied us that Lamarck was in 

 error in approximating Pleurotoma to Fusus : so strong 

 are early impressions and preconceived opinions. The 

 discovery, however, of the genus Crassispira brings 

 into this group, by means of the new genus Brachytoma, 

 a small group of shells, having the aspect of some 

 Lamarckian FusincE, but with the basal canal longer, 

 and the spire shorter, than Crassispira. One of the most 

 typical has been aptly named St7'ombiformis* ; it is tur- 

 reted and nodulous, with the notch at the top of the 

 outer lip short, and nearly semicircular, — hardly more 

 developed, in fact, than it is in Crassispira. There are 

 several other species, mostly nodulous, and having the 

 general appearance of such shells as Fusus Syracusensis. 

 We next come to the typical genus Pleurotoma, where 

 the channel is so much lengthened as to be little shorter 

 than the spire. These appear to be succeeded by a group 



* Sow. Manual, fig. 381. 



