114 COLLIXGE : STRUCTURE AND AFFINITIES OF EUROPEAN SLUGS. 



external morphology. It is only necessary to allude to the 

 re-establishment of Nilsson's Arion fasciatus 1 for what has since 

 been termed A.circumscriptus, Johnst., A. bourguignati, Mabille, and 

 A. ambzguus, Poll., and to the placing of the Limax anereo-niger. 

 Wolf, 2 as a variety of L. maximus, L., to illustrate my argument. 

 In placing a sole reliance upon the reproductive system, I see 

 a danger — it is upon this system that most of the species during the 

 ast few years have been founded — fairly constant as it is, certain 

 slight anatomical variations are constantly occurring, as well as the 

 comparatively unimportant ones due to age, season, habitat, <\:c., 

 and if we are to arrive at conclusions of any value, malacologists 

 must agree to allow a species to vary within a certain range, and to 

 place less reliance upon the external morphology and lingual ribbon. 

 Unless this is done, the malacologist of the future will be surrounded 

 by a burdensome nomenclature and innumerable difficulties. The 

 shell, in the slugs, is likewise of little or no service for generic or 

 specific distinction, being liable from many causes to great variation. 

 In the Tcstacellidic and Limacida. far too much importance has been 

 attached to this structure. 



Whether we shall ever agree upon a more rational method of 

 creating new species of the Mollusca in this country it is difficult to 

 say, but, I think it is slowly but surely occurring to many, what 

 a great waste of time and energy is being spent by malacologists in 

 this country upon purely secondary systematic points, and the little 

 attention bestowed upon the more important morphological and 

 embryological ones. 



Our knowledge of the European slugs is mainly due to the works 

 of Simroth, Lessona, Pollonera, and Baudon, and if we hope to 

 arrive at any true knowledge of those of our own country, it must be 

 by careful comparisons with the Continental forms. I hope from 

 time to time to describe in the " Conchologist " the more interesting 

 forms that pass through my hands. For most of the specimens here 

 described, I am indebted to the kindness of Signor Carlo Pollonera, 

 of Torino, and for whose valuable criticism and assistance I offer 

 my best thanks. 



Arion subfuscus, Drap. 



Locality: Vegesach bei Bremen. 



These specimens were smaller, darker, and more uniform in 

 colour than any specimens I have seen in the British Isles. 

 Signor Pollonera informs me, however, that it is a species which, in 



1 Conchologist, 1892, ii., p. 77. 



- Annals and Mag. N.H., 1892, p. 425. 



