166 Mr. J. G. Jeffreys on the Marine Testacea 



objects increases, and greater difficulty consequently arises in 

 separating and distinguishing them from each other; the line 

 of demarcation becomes more and more faint, and the naturalist 

 is tempted, not only to distrust the distinctiveness of certain 

 characters which he had before regarded as sheet-anchors, but even 

 to doubt the possibility of establishing any characters at all. This 

 phase is ultimately succeeded by more or less critical views, 

 dependent on the idiosyncrasy of the naturalist, as the sphere of 

 his observation is extended ; and he is then, by a sort of innate 

 facility, able to discriminate species from varieties, and to assign 

 to each its proper and relative position. He finds that the 

 characters of distinctiveness vary in the different groups or 

 genera and species ; that diffei'ences of a more or less important 

 nature, such as form, size, colour, and appendages, arise from 

 locality, food, and other causes, and only constitute varieties; 

 and that there is an inherent tendency of all species to adapt 

 themselves to certain changes of condition, and to undergo 

 transformations of frequently the most Protean kind. The dis- 

 crimination of species and varieties is one of the most important 

 duties of the naturalist, because, without it, the study of nature 

 would lead to no result, and there would be no precise data from 

 which any conclusions could be safely drawn. The facility or 

 habit of such discrimination depends on both synthesis and 

 analysis, and is only attainable by practice and a large sphere of 

 observation. Hence, local naturalists do not in general possess 

 this quality ; the usual form of their error being to split species, 

 and attach too much importance to minute differences. The 

 necessity of rigorous discrimination of species and varieties 

 cannot, indeed, be too much or too frequently insisted on. 

 Messrs. Hooker and Thompson, in the introductory essay to their 

 recent and valuable work entitled 'Flora Indica,' which abounds 

 in philosophical views and remarks as to species and varieties 

 of plants, say with justice that " the discovery of a form uniting 

 two others previously thought distinct, is much more important 

 than that of a totally new s])ecies, inasmuch as the correction 

 of an error is a greater boon to science than a step in advance.^' 

 It is unquestionable that the soft and hard jDarts of the 

 Mollusca are of relative and nearly equal value ; the former 

 for generic, and the latter for specific distinction. Both must 

 be studied in relation to each other ; and it seems to me most 

 illiberal in the malacologist or conchologist to ignore or depreciate 

 the labours of his brother-naturalist. Philippi, in the second 

 volume of his ' Fauna Molluscorum utriusque Sicilise,^ after 

 stating that Bivona had seen the animals of several species of 

 Rissoa, and that he had himself figured the animals of other 

 species, concludes with this remark, " Hse species omnes simil- 



