1922. No. 5. 



ARIONIDAE OF NORWAY, 



of the cone appears to be attached to 

 the inside of the atrium along a Une 

 shaped ahiiost like a horseshoe. 



The spcrniatophorc attains a 

 length of 3 cms., bears a denticulated, 

 spirally running list, and has a slen- 

 der tail. 



Variation. A most interesting 

 feature in Arioii atcr is the abundance 

 of different coloured varieties, some 

 of which are splendidly depicted in 

 the monograph by Taylor quoted 

 above. In Norway only the black var. 

 atra and the white var. alba are com- 

 mon, but there are also rarely found 

 the red var. ntfa and the chocolate- 

 coloured var. castauca, as well as some 

 multi-coloured varieties. To clear up 

 the mutual relation of these forms ex- 

 perimental investigations are necessary, 

 but as yet only faint indications to this 

 end have been undertaken. Collixge 

 (1909) and KCxKEL (1916I have shown 

 that some varieties mate together and 

 that from one variety others may be 

 derived. A certain degree of influence 

 bv external factors, for instance by 

 temperature, has been shown. 



\'ar. atra L., Syst. Nat., ed. 10, 

 1758, p. 652. 



Liiiiax atcr L., op. cit. 



The back and the sides of a 

 uniform black colour, the middle part 

 of the foot-sole usually paler than the 

 lateral ones, but sometimes even of 

 the same dark colour (and then di- 

 stinguished as a distinct variety by 

 Taylor). 



This form (PI. 1, i) is most charac- 

 teristic on the stretch of coast from- 

 Trondhjem to the Kristiania Fjord, and 

 is there ("\^estlandet" and "Sorlandet") 

 to be seen in large numbers on roads 

 and fields during rainy or cloudy 



Vid.-Selsk. Skrifter. \. M.-N. Kl. 1922. No. 5. 



Fig. II. Lower parts of the reproductive 

 organs of immature Avion atcr, ' \. 



atr. atrium genitale, ep. epiphallus, /. r. 

 lateral recess, o. oviduct, o.-sp.-d. ovi- 

 spermatoduct, rcc. receptaculum, retr. re- 

 tractor, v.d. vas deferens. 



xKAi. hJlßv. 



Fig. 12. Lowest parts of the reproductive 

 organs of Arioii atcr var. media, ^ 1 . 



atr. atrium genitale, cp. epiphallus, /. /-. 



lateral recess, o. oviduct, st. rcc. stalk of 



the receptaculum, vest. retr. vestibular 



retractors. 



