1902] The Holotlinrioidea of Northern NorAvay. 15 



other, up to 200 -300 per 10 □ ii^™- G^enerally there are also 

 wheels scattered even on the foremost thirdpart of the ventral 

 surface, somethnes a few even on the other part of the same. The 

 wheels are so hig, that they can be seen by the naked eye as small 

 dots on the skin. The average diameter of a great number of 

 wheels, I found to vary in different specimens between 0.205 

 and 0.260 mm. In every specimen some wheels are of course to 

 be found, the dimensions of which are more aberrant, but very few 

 indeed smaller than 0.140 mm. or larger than 0.280 mm. The 

 spokes of the wheels, with the exception of monstrosities, are (12 — ) 

 14—25, the teeth on the periphery of the wheels 21 — 35. 



The wheels are placed so very close to the epidermis that 

 their teeth make the surface rough. Non-contracted specimens are 

 as a rule 4 — 7 cm. long and 6 — 12 mm. thick. The largest dimen- 

 sions are met with in the high arctic regions. 



The above statements are based on a very rich material, mostly 

 from the Zoological State Museum in Stockholm. Like many other 

 species, which are widely distributed, il/. rinMi shows some small 

 differences in different parts of the district, in which it is found. 

 In specimens from East Siberia I found, for inst., the average diame- 

 ter of the wheels as a rule vary between 0.240 and 0.260 mm., 

 while it in others generally keeps between 0.205—0.235 mm., in 

 the Norwegian specimens which I examined between 0.208 — 0.220 mm. 



In all the Norwegian specimens the wheels differed by a very 

 small number of spokes. In the specimens from Yadso they were 

 (12—) 14 — 18, upon an average 15, per wheel, in specimens from 

 Kvænangen and Lyngen 14 — 19, on an average 17.1. In specimens 

 from the high arctic regions (different places in Greenland, Spitz- 

 bergen and Siberia, for inst. 76^ 52' N., 116° E. and 70° 14' N., 

 170^ 17' E.) the spokes are on the contrary 16 — 25, averaging as 

 a rule about 20. The number of the teeth are, on the other hand, 

 not at all diminished in the Norwegian specimens, averaging in the 

 different specimens 26.5 — 29.3 per wheel. The number of the 

 spokes are therefore in this case not much more than half of that 

 of the teeth, or more correctly 54 — 60 ^/o. In the high arctic 

 specimens the number of the spokes is about V4 of that of the 

 teeth, or 74—81 7o (in some young specimens, however, only 69 7o). 



A decrease in number of the spokes seems to take place 

 even at other places, which are situated on the border between 

 the Arctic and Boreal regions. Thus the spokes in specimens from 



