64 COLL1NGE : REVIEW OF THE ARIONID/E OF THE BRITISH ISLES. 



Arion mabillianus, Baudon, Trois. catal. Moll. Oise, p. 8, 1884. (Not 

 A. mabillianus, Bgt., 1866). 

 ,, flavus, Clessin, Deut. Excurs. p. 116, f. 55, 1884. 

 ,, minimus, Simroth, Zeit. f. wiss. Zool., p. 2891, 1885. 



Body white, light-yellow or grey ; head and tentacles dark grey ; 

 lateral bands faint or absent, diffuse on mantle ; ruga; have 

 minute conical spikes ; foot, white, appears yellow, due to 

 slime. 



This, the smallest of our Arions, was first identified as a British slug 

 by Dr. Scharff (34) in 1890. Like A. empiricorum it assumes the 

 peculiar arched position when at rest. Although priority rests with 

 Normand, as far as the actual name is concerned, Simroth (39) was 

 the first to re-establish its claim to rank as a species, on anatomical 

 grounds, in 1885.* 



Mabille (23), Drouet (15), and Baudon (2), have all classed this 

 species as a Geomalacus, chiefly from the fact that the calcareous 

 granules are sometimes found congregated together, and thus forming 

 an irregular shell. 



The rugae are very peculiar in this slug, the apex of each forms 

 a minute knob-like projection or spike. In most of the specimens 

 I have examined, the lateral bands have been absent ; they are never 

 very prominent however, and always diffuse. 



Anatomy. — The vestibule is large. Like A. subfuscus, it has the 

 oviduct and prostate short. The free portion of the oviduct is short 

 and shows no bend, as in some species. There is but little difference 

 in the upper and lower portions of the vas deferens. The recepta- 

 culum seminis is generally of an oval form, being of greater width 

 than length. 



Reproduction. — I have not been fortunate enough to breed 

 this form as yet, but my friend Dr. Scharff (35, p. 550), who has been 

 more successful, describes the eggs, See, as follows : — "The clusters 

 of eggs which I observed very frequently in August and September 

 never exceeded twenty. The eggs are remarkably large for the size 

 of the slug, being 2 mm. long by ii mm. broad. The young ones 

 of 8 mm. in length, which I bred in captivity, were of a light-grey, 

 owing to the intestine being visible through the semi-transparent 

 walls of the body. The head was of a delicate grey, and no bands 

 were visible on the body or mantle. Still younger ones, of 3 mm. 

 long, were of a very light red, with violet tentacles, and had emerged 

 from the egg three weeks after their deposition." 



* It is very questionable whether descriptions of new species omitting an account of the 

 anatomy can be termed adequate, and malacologists are rightly refusing to recognise 

 inadequate descriptions, or descriptions of shells apart from the animal. 



