COLLINGE: A REVIEW OF THE ARIONID/E OF THE BRITISH ISLES. 79 



better accept it for what he has described as A. ambiguus, which 

 he states is an Avion kourguignati not keeled. Mr. Cockerell has 

 also suggested " that it is perhaps not unlikely that A. circumscriptus 

 was founded on A. ambiguity rather than A. bourguignati proper," 

 but he thinks that both the British and Continental forms are 

 specifically identical. Reference to the anatomy will alone solve the 

 problem whether these three slugs are each distinct species or forms 

 of one species. I have not the slightest hesitation in saying that 

 the internal anatomy of the three is identical. Forms of 

 A. bourguignati received from Pollonera have been compared with 

 the A. circumscriptus and A. ambiguns found in this country, and 

 I fail to see any distinctions worthy of note that would specifically 

 separate them, therefore, we have no alternative but to accept these 

 three names as synonyms of A. fasciatus, Nilsson, for the type of 

 this author was certainly an Arion bourguignati. 



Like A. empiricorum, etc., it assumes, when tapped upon the 

 head or an attempt is made to lift it, the peculiar arched form. 



Anatomy. — Whilst showing affinities with A. kortensis, there 

 are certain well marked and permanent characteristics. The single 

 vestibule is large and well developed. The free oviduct is short 

 and seldom exhibits a broad and narrow portion. The vas deferens 

 is considerably longer than in A. Aoriensis, slender in the upper 

 portion, dilating a little in the lower end, but very rarely, if ever, 

 exhibits swollen portions at its juncture with the vestibule. The 

 receptaculum seminis is elongated, terminating in an attenuated 

 apex, quite distinct from any other British Arion. 



Reproduction. — The eggs are deposited from April to July. 

 The young forms are often of a light-yellow or straw colour, as 

 described by Johnston (22). 



Variation. — There are three well marked varieties in Britain, 

 viz., a brown, a yellow, and a silver-grey form. 



a — neustriacus, Mabille. This and the variety c seem to be the two 

 forms generally met with in the British Isles. The var. 

 subfusca, Roebuck, is synonymous with this. 

 B— -flavescens, Cllge. (11). A not uncommon form, 

 c — var. nov. griseus. Animal a light silver-grey with darker grey 

 lateral bands. Bourguignat named a figure of Ferussac's 

 A. hortensis, as var. grisca, which is probably a form of 

 A. fasciatus and not iiortensis. Descriptions of figures, in my 

 opinion, are not admissible in any rational system of 

 nomenclature, and as the grisea of Bourguignat does not seem 

 to have been since recorded, I am describing the above, 

 which, as far as I can learn, is not found on the Continent. 



