1922. No. 5. ARIONIDAE OF NORWAY. 



However, the groupe AiiiDicithis has not been accepted as a genus, 

 but has been given the rank of a subgenus, and later on Arioii iiitcrnwdiiis 

 owing to the position of its orißcinm genitale was placed here. But from 

 the anatomy of the Norwegian stock recently discovered, it is evident that 

 this character is not constant even in the same species. The fact is that 

 the descriptions of Avion intenncdiits in other countries state the genital 

 aperture to be situated anterior to the respiratory orifice', often at the same 

 distance from the latter as from the base of the right ommatophore, while in 

 all Norwegian specimens it was close to the split of the respiratory orifice 

 (fig. i). How little systematic value this original generic character has is ob- 

 vious, also, from the position of the genital porus in Arioii circiiiiiscriptus. 

 In this species all Norwegian specimens examined had the latter at a con- 

 siderable distance before the respiratory orifice (fig. 1 1, a point that has 

 perhaps been overlooked in the foreign stocks. Consequently, the position 

 of orificiiuii genitale perhaps xaries also in this species. 



This degradation of a character, at first interpreted as a generic one, 

 is a rather instructive example of the variation in the Avions, proving how 

 a closer investigation will often discover connecting links between types 

 that at first were considered to be quite separate. 



As regards the historic systematics of the species, it may be mentioned 

 that SiMROTH (1885) gave a description of it under the significant and much 

 applied name, Avion niininuis [niininuis — smallest), but rejected it, in 

 1907, admitting that the name of Normand had priority, the latter author 

 having designated the species as Liinax iutciiiicdiiis {infej-inec/i/is — inter- 

 mediate) as early as 1852. 



Description. External characters (fig. i and PI. I, 81. 



Avion intevniediiis is the smallest of the Norwegian Avions, never 

 measuring more than 2V 2 cms. fully extended; generally it is not even so 

 long. The colour is from white to pale yellowish grey, with the back and 

 the head a little darker, the ommatophores especially having a dark pig- 

 mentation. In that respect it may be rather like the young of Avion atev, 

 but there are good external characters which prevent confusion. In the 

 living animal it is most peculiar that, when contracted, the tubercles look 

 like small spikes; further the foot-sole is yellow. In alcohol material, how- 

 ever, both characters will be found at fault, and the following should then 

 be looked for. Very often there are some little black points in the anterior 



anse ben distinte. Nella mandibola vediamo che I'Ariunculus ha solo la parte centrale 

 munita di coste ben distinte, mentre negli Anon le coste la occupano quasi intera- 

 mente. A queste differenze anatomiche io non do un peso eccessivo, ma avendole 

 notate in tutto tre le specie che compongo il mio nuovo genere ho creduto bene di 

 metterle in evidenza." (Pag. 196I. 



Vide the Monograph of Taylor, p. 241. Perhaps the German stock more resembles 

 that of Norway, to judge from Simroth (1885, p. 290): „In einem Falle konstatierte 

 ich freilich die unmittelbare Nachbarschaft von Athemloch und Genitalporus". 



