ScHAEFF — On the Slugs of Ireland. 545 



Arion hortensis, Fdrussac. 



Arion hortensis, F^russac, Hist. IIolL, 1819. Arion hortensis (pars), Jeffreys, 



Brit. Conch., 1862. 



(Plate LVI., fig. 20.) 



Colour of body generally dark gray or light brown, with bluish-gray sides. 

 Lateral bands somewhat diffuse towards sides of body, always present, and con- 

 tinued to front of mantle. Foot always red, wrinkles broad. The calcareous 

 grains composing shell often more aggregated than in other species. Receptaculum 

 seminis round. 



External Characters. — A typical form of this slug is at once recognized from 

 other species by the red colour of the margin, as well as the sole, of the foot. But 

 the intensity of this colour is subject to a good deal of variation, and in many cases 

 the foot is more of a yellowish colour, with just a tinge of red, while sometimes 

 only a faint indication of colouring remains. In such cases A. hortensis might well 

 be mistaken for one of the other species. By a little practice, however, we can 

 soon detect other distinguishing characters. 



If we. take an A. hortensis of 20 mm. in length, and compare it with specimens of 

 A. ater (PL LVI., fig. 16) A. hourgidgnati (PI. LVI., fig. 21), and A. intermedins (Plate 

 LVI., fig. 22) of the same length, the little conical wrinkles will at once eliminate 

 the latter. From A. ater the specimen of A. hortensis will be distinguished by its dark 

 colour, young ones of the former being always light-coloured ; the wrinkles, more- 

 over, in A. ater are longer and broader. Sometimes A. hortensis is remarkably like 

 A. bourguignati, but apart from the wrinkles, which are broader in the former, the 

 lateral bands are somewhat diffuse towards the external edge, as if they had been 

 touched by a wet brush, whilst in A. hoiirguignati their edges are well defined. 



If spirit specimens of the same size are taken, which sometimes have lost all 

 trace of colour, the wrinkles must decide, and, of course, as a last resource, the 

 anatomy. If we measure the width of the wrinkles just behind the mantle, we find 

 that in A. ater rather more than one, in A. hortensis two, and in A. bourguignati three 

 wrinkles go to the millimetre. 



So much for comparison. As for the general colour of this species, I find that 

 two distinct varieties are as a rule found in the garden. The back of the body and 

 mantle in the first is of a dark gray, becoming lighter towards the lateral bands. 

 Below these the body is of a light, sometimes bluish-gray colour. 



In the second variety, which was much more numerous in my garden in Sep- 

 tember, the back of body and the mantle were as if dusted over with fine yellowish 



TKANS. ROY. DUB. SOC. N.S. VOL. IV., PAET X. 4 G 



