1922. No. 5. 



ARIONIDAE OF NORWAY. 



41 



Jaw : similar to Arion circtiiiiscripttis, but often of a uniform, slightly paler yellow 

 colour; from about 6 to 12 slender, partially indistinct ribs. 



Radula : often very similar to that ,of Arion subfuscus and Arion circiiinscriptns, but 

 can often be identified by the single cusp of the inner marginal teeth (no ectocone). 



Reproductive organs : the lower half of the oviduct conically dilated, its whole length 

 about the same as vas deferens — epiphallus. The latter conical, with a distal bulbous 

 enlargement. 



Historical systematics. In spite of its rather characteristic appearance, 

 this species has been confused with others. In Scandinavia even recently 

 this name was appHed to Arion circiiiiiscriptiis, though in reality Arion 

 /lorfoisis occurs only in a few, scattered localities. In Norway, for in- 

 stance, all the collections of O. S. Jensen, Birgithe Esmark and Z. A. 

 HoYER preserved in the zoological Museum at Toien, are defined and for 

 the greater part published as Arion /lorh'/isis. At a later period this species 

 was recorded as common in the neig^hbourhood ot Kragero bv TioeMAND- 



Fig. 35- Fig. 36. 



Jaw of Arion Iiortrnsis, 34 1 j^w of young Arion liortensis, ^'^ I . 



RuuD (1898), a statement which perhaps needs verifying. As a matter of 

 fact, however, after I happened to find it in several places, the species 

 proves to occur in Norway only in quite restricted localities, such as in 

 certain parks, even if there very numerously. 



Description. External characters (fig. i and PI. I, 7). 



When extended the slender body of this species difters considerably 

 from the other, more clumsy Norwegian Arious. It attains a length of 

 about 4 cms. The colour in the fully developed specimens is of a peculiar 

 darkish brown, owing to the narrow yellow tubercles combined with the 

 dark ground colour; in alcohol, however, they turn bluish black like the 

 living younger specimens. Generally there is a narrow paler stripe inside 

 each of the black lateral bands ; the sides may either be pale, or, more 

 rarel}^, with the same black pigmentation as the lateral bands. 



An excellent character is afibrded by the orange foot-sole, the intensity 

 of the colour, however, varying in the same individual. At any rate in 

 Norwegian specimens the middle longitudinal part of the foot-sole is 

 often pale. 



When preserved in alcohol this species is often very similar to Arion 

 circuniscriptiis, especially as to its var. nigra, and then the course of the shield 

 bands is a most valuable criterion, in anv case alwavs reliable in Norwegian 



