466 Mr. J. G.Jeffreys on Chemnitzia and other Mollnsca. 



that although he haa so sedulously and with such scrupulous 

 delicacy avoided any mention of my name, I have not the least 

 fear of imperilling our old friendship (now of more than twenty 

 years' standing) by the discussion ; and that no quotation from 

 Lucretius or any other author, ancient or modern, was necessary 

 to remove any " bitterness " of feeling which he might have an- 

 ticipated on my part. As however I have neither time nor taste 

 for a lengthened controversy in your valuable Magazine, I do 

 not mean to say more at present on the subject. ' 



.ffo;With respect to the separation of these shells into more genera 

 than one, I defer to the authors of the ' British Mollusca,' who, 

 from their more extensive opportunities and superior knowledge 

 of the subject generally, must be better qualified to give an opi- 

 nion than Mr. Clark or myself, who after all cannot be regarded 

 in any other light than as local amateurs. 



But in the distinction of species a difficulty of coui'se suggests 

 itself in the first instance, as to what is a species, in this or any 

 other defined or recognised group of Mollusca. It seems to me 

 that one of the chief tests of such distinction which is applicable 

 to the case of higher or more organized animals (the fecundity 

 of mule or hybrid individuals) must be wanting in the marine 

 Mollusca, owing to the extreme difficulty, if not impossibility, of 

 observing the succession of their races. Besides, the animal in- 

 habitants of molluscous shells offer very insufficient criteria for 

 the distinction of species, unless the hard parts or shells are also 

 taken into consideration ; and if the character of the soft parts 

 (which is seldom appreciable if perceptible) were to form the 

 only test of distinction, most of the species of any group or genus 

 would be reduced to limits narrow enough to satisfy even my 

 Procrustean friend Mr. Clark. It would be as just to take the 

 soft parts of the Crustacea or Echinoderms and attempt to clas- 

 sify them without regard to their covering. This would be doing 

 equal violence to nature as to truth. In a conchological point 

 of view, the value of specific characters differs in almost every 

 genus ; and the knowledge of the laws which govern this varia- 

 tion can only be acquired by extensive and not local study, how- 

 ever perfect of its kind the latter may be. 



f)tS It is evident that Mr. Clark in his remarks on the species 

 does not place any reliance on his own faculty for distinguishing 

 one from another ; as he admits having changed his opinion no 

 less than three times about the Odostomia iurrita of Hanley. 

 The admission was made with his usual candour ; but it might 

 cause some of his readers to think that he may be doing more 

 harm than good to the cause of science in unsettling the minds 

 of " students " by such doubts. With this impression on my 

 own mind, I cannot subscribe to his dogma, that the question 



