45 

 t 



our island fauna. In it lie has added to the list about 30 

 species not embraced in Mr. Legrand's monograph, 4 of which 

 were described by the Eev. J. E. Tenison-Woods, 17 by Mr. 

 Petterd, 3 by Capt. Beddome, and one small but unique 

 species by myself. Perhaps, however, the greatest credit is 

 due to him for the effort to remove the difficulties, day by day 

 on the increase, in connection with the existing classification. 

 Many of the shells erected into specific distinction by 

 Dr. Cox and others, require revision in the light of 

 experience derived from the accumulation of large numbers 

 of individuals, under various circumstances, and from 

 many widely separated localities. Some of the species 

 were described from single, or, at most, two or 

 three individuals, and the extreme variability of certain 

 forms has been the cause of confusion in that one or two 

 varieties have been erected into specific distinction from im- 

 mature specimens. As no one, however, can tell to what 

 extent certain groups vary from one or two individuals, such 

 mistakes are not only pardonable, but, if the descriptions are 

 merely considered provisional, they are, historically, of the 

 greatest advantage. 



It was to be anticipated, therefore (indeed the authors state 

 as much), that when other districts and a larger series of in- 

 dividuals were obtained, it might be necessary to reduce the 

 number of species. 



Until this was done it was impossible to say wl; it were 

 characters of specific value and what were not. It must not, 

 therefore, be supposed that any reasons now adduced in support 

 of the claims for a reduction of the number of species are in- 

 tended to reflect upon the valuable work already done by those 

 who had to do the best they could with scanty material. It is 

 not an easy matter to tell what characters are of specific value 

 and what are not even when the fullest information has been 

 obtained as to the variability of the individuals of a group, 

 and the greatest living authorities often come to different 

 conclusions. It would be unreasonable, therefore, to expect, 

 in the absence of the fullest knowledge respecting variation of 

 size, colour, sculpture, distribution, that any author could 

 determiue, with accuracy, those characters which alone should 

 entitle certain shells to specific rank. Of course I am aware of 

 the difference of opinion which existed, and which even now 

 exists in a more modified form, with respect to what consti- 

 tutes a species and what a variety ; but there is now, with 

 few exceptions, sufficient agreement among the leading philo- 

 sophical naturalists to leave little room for doubt in cases 

 where the definition of a species is based upon the observation 



