NATURAL CLASSIFICATION OF THE GASTEROPODA. 161 



On the Natural Classification of Gasteropoda. — Part I. 

 By Dr. J. D. Macdonald, K.N., F.E.S. 



[Eead June 17, 1880.] 



In the year 1860, just twenty years ago, Professor Huxley com- 

 municated to this Society a paper of mine, on the " Classification 

 of the Gasteropoda," founded respectively, 1st, on the sexual 

 characters, 2nd, on the lingual dentition, and 3rd, on the auditory 

 concretions ; and, notwithstanding all that has been done of late 

 years in this department of natural history, the General Table 

 then given would still appear to hold its ground as a natural 

 arrangement. 



The object of this paper is to add some additional remarks and 

 suggestions to the former one, adopting a fourth guide to the dis- 

 covery of natural affinities, namely, "Representative Relation- 

 ships." 



The faculty of comparison should be well developed in the sys- 

 tematic naturalist ; but we often find that it is misapplied, and 

 superficial resemblances are assumed to be indications of genuine 

 affinity, so that, apparently, like things are grouped together, 

 though intrinsically bearing no natural alliance to each other. 

 Indeed, underlying nearly all the mistakes that have been made in 

 matters of classification, we find the occurrence of representative 

 relationships or analogous characteristics repeating themselves 

 in particular members of the orders, suborders, families, or even 

 smaller groups of the Animal Kingdom. The recognition of such 

 representative relationships, as distinguished from those of affinity, 

 must depend upon a more general comparison of structure. Thus, 

 breathing in air, for instance, can be easily shown to be a repre- 

 sentative character amongst larger groups, and, of course, of 

 great importance in neighbouring species ; but it can by no means 

 warrant the association of the members of two otherwise quite 

 distinct groups. Yet, if we analyze the JPulinonifera of authors, 

 what do we find ? First, that all air-breathers are placed in one 

 category ; secondly, that they are recognized to be either operctdate 

 or inoperculate ; and, thirdly, that the momentous question of being 

 monoecious or dioecious is either not noticed at all, or referred to 

 in a casual way, the latter being indicated by the presence and 

 the former by the absence of an operculum — though, unfortu- 

 nately, some Diplommatinee, which are unisexual, are inoperculate, 

 and the anomalous bisexual genus AmpMbola is furnished with an 

 operculum. 



