﻿CONCLUDING REMARKS. 



191 



vertical horizon as, the place of their former occurrence. On the other hand, some of 

 those previously considered rare have become more plentiful. 



In my list will be found many species to which my name is attached. Some of these 

 will hereafter probably require to be altered through having been described by others 

 previously to my work, but I have relinquished my own names wherever, up to the present 

 time, I felt satisfied of the identity of my shell with any other previously described. In 

 every case where I thought it could be justly identified with any other, whether known as 

 living or not, I have not hesitated so to give it, suppressing, whenever occasion required, the 

 name under which it had been previously known from the Crag in favour of any earlier 

 name which the species with which it is thus identified may possess. After all this, 

 however, there remains a wide difference between the view taken by me of the Crag 

 Mollusca, and that taken by the author of the ( British Conchology indeed, while according 

 to that author my tribute of admiration for the persevering industry with which he has 

 so much enlarged our knowledge of the Mollusca of British seas, and of the waters 

 adjoining them, I do not hesitate to point out what, in my judgment, impairs the 

 conclusions he has expressed with reference to Crag species, both in his general work, and 

 in those lists of which he is the author which form part of Mr. Prestwich's papers on 

 the Crag already referred to. It is obvious that this author's leanings are very marked, 

 so as to group together allied Crag forms as varieties only of one species, and especially 

 to make out a Crag shell to be either identical Avith a living species, or, at most, 

 only a variety of it wherever the slightest presumption can be found for that course. I 

 observe, how r ever, that this reluctance to recognise two distinct, but allied, Crag forms as 

 anything more than a variety gives way when the form has been found living ; and I have 

 been particularly struck with this in the case of Scalaria subulata, which in the first, or 

 ' Cor. Crag List,' is put in italics as a variety only of Scalaria foliacea, but which in a 

 note to the ' Red Crag List ' (page 496), is restored to specific importance in consequence 

 of its having in the meantime been dredged living by Mr. McAndrew. The degree of 

 difference which is to constitute a species must in a great measure be arbitrary; lout there 

 are many shells of the Crag thus identified with living ones which show quite as little 

 variation from shells of the Older and Middle Tertiaries as they do from their living 

 analogues. If species arise, as I believe they do, by gradual variation from forms 

 previously existing 1 (be the cause of that variation what it may), it is obvious that, if we 

 could get a perfect collection of all the forms that have existed and do exist on the surface 

 of the earth, we should be placed in the dilemma of not being able to draw a specific line 

 anywhere ; and although it must be a long day, if ever, before such a knowledge of animal 



1 In a letter to me (April 27th, 1873) the author of the ' British Conchology' says, " I believe not in 

 evolution, but in descent with modification ;" and I observe the same phrase — " descent with modification " 

 used by his colleague in the "Porcupine" dredging expedition, Professor Thompson, in his late 

 work, 'The Depths of the Sea' (page 480). I confess that I do not understand the difference between 

 this and evolution, in which I have for very many years been a believer. 



