^4* SHELLS AND SHELL-FISH. PART I. 



more remote and faint than those which relate to the 

 aberrant divisions^ — and for this simple reason; — the 

 typical groups are furthest apart from each other ; 

 while the aberrant ones, by which they are connected, 

 are consequently nearer. In this branch of science, 

 moreover, the difficulty of discovering the analogies 

 of typical groups is still further increased, when, as in 

 the present instance, we are without that precise in- 

 formation on the animals, which might furnish us with 

 some analogical points of resemblance. Besides, it 

 must always be borne in remembrance, that our ar- 

 rangement is not built upon these analogical compa- 

 risons, but upon absolute or presumed affinities, the 

 result of minute analysis. Whatever coincidences, 

 therefore, arise on comparing the different groups, are 

 more properly the result than the cause of their ar- 

 rangement. Analogy is thought to be of the highest 

 importance for the verification of a natural group, but 

 it must always be subordinate to affinity. Applying 

 these general remarks to the two typical groups which 

 stand first upon our list, it will be remembered that 

 one, intervening between Turbinella and Fasciolaria, 

 has never been made known. Passing these, however, 

 and comparing Fasciolaria and Hemifusus, we find 

 they are almost precisely of the same shape and pro- 

 portions ; and that the shells can only be distinguished by 

 one having the pillar plaited, and the other smooth. 

 The very name of ficulneus, given by authors to the 

 type of Strepsidura, shows its analogy to Pyrella, and 

 consequently to Fyrula ; it is, in fact, completely a pear- 

 shaped shell. The resemblance of Clavalithes and 

 Leiostomvs is equally striking : both are remarkably 

 smooth shells ; with the channel lengthened, and the 

 basal volution more or less enlarged ; both are fossil 

 genera of the same strata; and although Clavalithes in 

 general possess very small plaits on the pillar, and a 

 papillary spire (without which, in fact, the genus could 

 not be clearly defined), yet there are one or two species 

 having the pillar, as in Leiostomus, perfectly smooth. 



