I Kil) I irjOl- OKI. AM). 



.M.-N. Kl. 



knowledge. lie divide.s tlie species intf) live- groups, ;in(l the- types of these 

 are just tlie- five species of tiie fauna of Norway. 



Description. External c h a r a c t e r s . Most of the ylrions have a 

 rather corpulent body, broader than in tin- other family of Norwegian slugs 



/. r. the Linincidac. As in other ter- 

 restrial air-breathing gastropoda, the 

 skin of the upper side is traversed by 

 a system of cro.ssing lines, and is thus 

 divided into numerous tubercles. The 

 must marked of these lines extends 

 from the transverse opening of the 

 supra-pedal gland close to the under 

 side of the head, running backwards 

 along the lower part of the sides to 

 the characteristic triangular tail gland. 

 Thus the lower part of each side is 

 separated from the upper part in the 

 shape of a narrow stripe, forming the 

 socalled foot-fringe. Anteriorly the back 

 is covered by the mantle or "shield", 

 which is rounded at each end and 

 superficially shows a granulated struc- 

 ture. In front of the middle of the 

 right side of the shield we find the 

 respiratory orifice or the pneumostome, 

 from which runs a split sloping for- 

 wards. In the lip of the pneumo- 

 stome is the common opening of the 

 alimentär}^ canal and the kidney. The 

 genital orifice is close under the pneu- 

 mostome or a little to the front of 

 it (fig. i). 



The back is rounded from one 

 side to the other, and even though 

 the young have a dorsal keel on the 

 tail, this never appears in the sharply 

 compressed shape which is met w^ith in the genus Liiiiax. — The medial 

 part of the sole of the foot is indistinctly separated from the lateral ones. 

 Most of the species have a darker lateral band on each side, and even 

 in species where as a rule these are absent, they may, as in Arion atcr, 

 appear in some cases, especially in the young. As will be pointed out at 

 the end of this section (p. ii — 12), the shape of the lateral bands on the shield 

 as a whole proves to be very constant in each species, at any rate in the Nor- 

 vi^egian forms. I will therefore draw attention to this point in eases where 



Fig. I. Diagram of the shield-bands and 

 the position of orificimn genitale in the 

 Norwegian Ar ions: Arion a/er, A. stih/usciis, 

 A. circtmiscriptiis, A. iioriensis, A. inter- 

 ntedius. 

 pn. pneumostone, or. gen. orificium genitale. 



