1922. No. 5. 



ARIONIDAE OF NORWAY. 



37 



tube with low ribs outside, one of which is more strongly developed than 

 the other, and is denticulated. 



Variation. In contrast to the anatomical characters, especially to the 

 reproductive organs, the external characters exhibit a proportionally incon- 

 siderable variation. In Norway only two varieties are common. 



Var. circumscripta nom. n o \- . (PI. I, 4). 



The back yellowish grey with an orange band along the outside 

 of the dark lateral bands ; the sides of the 

 body pale. 



The orange pigmentation first appears 

 when the specimens are nearly full-grown, 

 and, though it is especially conspicuous outside 

 the dark longitudinal bands, it gives the 

 whole grey colour of the back a very faint 

 yellowish tinge. The younger specimens of 

 this variety are distinguished from the following 

 one by their pale sides. 



In Norway this is by far the most com- 

 mon form of the species, and, following the 

 usual practice, I have accordingly formed its 

 variety name in repeating the specific one. 



Var. nigra no v. var. (PI. I, 5). 



Both the back and the sides are from dark 

 grey to a bluish black colour; the back, and 

 especially the shield, mottled with little black 

 points. Mucus sezernated on the lower part 

 of the sides of a milky colour. As a rule 

 slightly smaller than var. circumscripta and 

 with more sloping sides. Otherwise similar to 

 the preceding variety. 



It may be pointed out that specimens in 

 alcohol are rather like Arion hortensis, but the course of the shield-bands 

 is quite different, the right one forming a curve to the upper side of the 

 respiratory aperture as usual in Arion circnniscriptus, although the outer 

 limit may be blurred by the dark ground colour; in the other species the 

 band is closer to the edge of the shield (fig. i). 



According to the descriptions this variety resembles var. Icncophaea 

 Normand, which, however, has pale sides, and perhaps var. grisca Col- 

 LiNGE, yet being considerably darker than the latter. 



It is often found together with the preceding variety, though in a 

 smaller number. For localities vide Appendix. 



Ab. flava nov. ab. (PI. I, 6). 



With no traces ot dark pigmentation, even in the eyes. The shield 

 is of a pale yellow, likewise the back and the upper part of the sides, as 



Fig. 34. Spermatophore of 

 Arion circiuiiscriptus, l^/j 



