1922. No. 5. ARIüXIDAE OF NORWAY. 3 1 



Bionomics. Arioii siihfiisciis occurs in many different places, but 

 woods, and especial!}' forests of conifers, must be considered as its most 

 characteristic biotope. It may there be collected under the loose bark of 

 almost every stump, and in autumn as many as half a dozen specimens 

 can be found feeding on a single fungus. Otherwise it may be seen in 

 many places that offer food and moisture. Refuse heaps may shelter many 

 large and well-fed animals. It has a larger distribution than the continuous 

 forests of conifers, too, both horizontally and vertically. It occurs on the 

 subalpine mountain slopes, and I have found it in the region of Salices, 

 in places where Bctula nana is a most characteristic mountain plant. 



As with the other Norwegian Arions the voung ones are capable oi 

 lowering themselves trom a branch or some such object bv the help of a 

 thread of mucus. According to Kew (1902) this power is especially strongly 

 developed, the animals even being capable of turning and crawling up again 

 along the thread. 



As to parasites the Norwegian specimens, too, may occasionally prove 

 to have a great many nematodes in their alimentary canal; the systematics 

 and bionomics of these one cm. long parasites, however, are unknown. 



For a long time Avion subfiiscns was considered to feed exclusively 

 on fungi, eating large holes especially in Riissula and Lacfarius deliciosiis. 

 But later on it has been stated to feed on several kinds of vegetables and 

 even on carrion. 



Copulation has not been described, though Kl'xkel (1916) has shown 

 that it breeds in captivity. I have only once found it /// copula, in the middle 

 of July (Horgjem, Romsdalen, ^^/7). According to the said author it attains 

 maturity at 8^ 2 — 9 months old, begins the deposition of eggs in June or 

 July, and for 2' 2 — 3 months it deposites 8 — 12 hatches. Each contains 

 from 7 to 53 eggs, and a single animal may deposit 291 — 341 eggs. These 

 are white or pale yellow, and are either globular with a diameter from 2,5 — 

 3,5 mill., or oval with a length of 3 — 4 mill, and a breadth of 2 — 3,5 mill. 



Some results of the investigations oï KCxkel as to the development 

 may also be mentioned. According to the temperature, the young hatch 

 after a period of 3 weeks to 3 months after deposition. The}' are then 

 yellow-white, 6 — 7 mill, long when extended, and some of them already 

 show faint lateral bands on the back and on the shield. Three or four 

 days later, all the young ones have dark lateral bands. When i — 2 months 

 old they are yellowish brown, the median part of the back and the shield 

 being dark. The mucus is then yellow. At an age of about 10 months 

 they have attained a length of about 5 cms., but they are not full grown 

 until a month later, and may then measure up to about 8 cms. They 

 attain the age of 12 — 13 months. 



As early as in May I have found large specimens, a fact which proves 

 how in Arion siibfiiscus even fully developed specimens may survive 

 the winter. 



