46 FKIDÏHJOF ØKLAND. M.-N. Kl- 



ever, these become very conspicuous, and the pale bluish colour changes to 

 a darker bluish grey; gradually the sharp keel on the posterior part of 

 the back dissappears. At an age of five months, the animals have obtained 

 the colour of the adult, the orange mucus then usually converting the 

 bluish grey ground colour to a dark brownish colour. 



Arion intermedius (Normand). 



1852 Lininx iitterynedius Normand, Descr. Lirr.ac. nouv., p. 6. 



1885 Arion tniiiimus Simroth, Zeitschr. wissensch. Zool., p. 289, pi. Vll, fig. 41. 



Diagnosis. External characters: 2 — 2'/2 cms. long, white or pale yellowish grey, often 

 with some minute black points in the anterior part of the foot furrow. In the living, con- 

 tracted animal the tubercles look like little spikes, otherwise like flat, almost regular hexagons. 

 Foot-sole yellow. Indistinct lateral bands, the right shield band with an enlargement enclosing 

 the respiratory orifice. 



Jaw : not to be distinguished from that of the two preceding species, at any rate in 

 the Norwegian stock; greatly varying, with 5 — 10 ribs. 



Radula : the median tooth has its mesocone excessively constricted at the base, and 

 the length of its lateral cusps is equal with or a slightly greater than the distance from 

 the outer anterior corner of the basal plate to the foremost point of the lateral cusp. 



Reproductive organs : varying greatly, but the stalk of the receptaculum always with 

 a basal enlargement, and the oviduct equal throughout, shorter than vas deferens ~ epiphallus. 

 The Norwegian stock has the genital retractor powerfully developed, the epiphallus with a 

 marked transition from the vas deferens, and (in adults) an almost spherical atrium opening 

 in the prolongation of the split to the respiratory orifice. 



Historical systematics. The species is now grouped with some 

 small species from southern Europe, forming the subgenus Ariiinculiis. 

 However, as a result of my disquisition this has been proved to be 

 erroneous, and the subgenus Ariunculus should be rejected. 



The group of this name was originally created as a genus to include 

 three new species from Piedmont (Lesson a i 881). The only generic 

 character distinguishing it from Arion was said to be the position of the 

 genital aperture, which, instead of being placed close under the respiratory 

 orifice, was situated far more anteriorly, nearer to the right ommatophore 

 than to the respiratory orifice. Some other features were mentioned, too, 

 but the author adds that he does not attach so much importance to them. ^ 



' It may be advisable to quote the original description: 

 „Ariunculus mihi gen. nov. 



In tutto simile all' Arion fuorche nella posizione dell'orifizio sessuale che invece 

 di essere presso I'apertura polmonare, è sul lato destro del coUo all' altezza del tentacule 

 oculifero e piu vicino a questo che all'apertura polmonare." (Pag. 193). 



„Riassumendo ora i caratteri anatomici interni nei quali il mio genere Ariunculus 

 si distingue dagli Arion, mi sembra si possano stabilire i seguenti. Nell'apparato ripro- 

 duttore : i la borsa copulatrice che sbossa non in prossimita délia guaina délia verga ; 

 2 la guaina délia verga non distinta dal canale déférente ; 3 ° la matrice con due 



