FRIDTHJOF ØKLAND. M.-N. Kl. 



II. Smaller forms (less than 7 cms. when extended). Usually longitudinal 

 dark bands on both sides of the shield. 



A. Foot-sole not markedly yellow (common species). 



a. Variable colour, usually from dull grey to yellow and dark reddish- 

 brown. No pale mid-dorsal line. Mucus dark yellow. P'oot-sole 

 faintly yellowish white. Usually with sliirldhtuuls, Ihr riij^ht one 

 a/closes the rcspii'ato>y afycrtun'. yh'ion siih/uscus. 



b. Colour generally either yellowish grey or bluish grey. Along the 

 the middle of the back a series of pale tubercles, especially distinct 

 in the young. Mucus never deep yellow. Foot-sole pure white. 

 The right shield-band is ou the upper side of the respiratory aperture. 



Arion circmnscriptus. 



B. Foot-sole remarkably yellow (less widely distributed species). 



a. More than 2,5 cms. (extended), colour bluish grey (in the young) 

 or brownish (in adults). Tubercles normal (flat). Shield-band black, 

 at the edge of the shield, yet often ivith a narron.' pale stripe outside. 



Arion hortensis. 



b. Less than 2,5 cms. (extended), from white to yellowish grey. Above 

 the anterior part of the foot-fringe there is generally a horizontal 

 row of dark points. Tubercles in the contracted, living animal are 

 like spikes. Shield-ba)ids indistinct but shaped as in Arion subfuscus. 



Arion intermedins. 



Key to the Norwegian Arions, from the reproductive 



organs.^ 



I. The atrium, which is often constricted by a furrow into an upper 

 and a lower part, contains a large, conically rolled up organ (the ligula) 

 attached near the base of the oviduct. This upper part of the atrium often 

 has a bag-shaped prominence (a lateral recess). The oviduct branch of the 

 genital retractor partially ensheaths the oviduct from the point of attach- 

 ment towards the atrium. Anon ater. 



II. Ligula absent or unconspicuous ; no lateral recess. Oviduct branch 

 of the retractor with no oviduct sheath. 



they are absent), at any rate in the Norwegian forms; but I need not point out that 

 a certain degree of practice is indispensable. However, I am disposed to think that 

 by using the skeleton-like illustrations in figure i, together with the non-diagrammatical 

 figures in the plate, it is possible, with few exceptions, to determine even fixed 

 material from external characters. Obviously, however, the young ones may present 

 difficulties. 

 • The oviduct is here the same as the free oviduct. It should be pointed out that very 

 young specimens can with difficult}- be determined by this key ; in the first place the 

 reproductive organs are small, secondly their various parts have not obtained their final 

 aspect; e.g. this is to a high degree the case as regards the atrium. 



