15 Hjalmar Ostergren. [Xo. 9 



the Newfoundland Bank (Lat. 45^ 59' K, Long. 51° 49' W., 100 m.j 

 were on an average 16.3 and in a specimen from Barents Sea, 

 about 250 km. off the Norwegian coast (72° 27' N., 35° 1' E., 

 249 m.) 16.9 per wheeh But while, especially in the specimens from 

 the Newfoundland Bank, even the teeth were fewer than usual, 

 the number of the spokes was respectively 70 and 64 % of these. 

 The relative number of the spokes seems therefore in a peculiar 

 way in this species to decrease, in proportion to its nearer approach 

 to the periphery of the Arctic region. 



It is worth mentioning that the Norwegian specimens have been 

 found only at greater depths (100 — more than 300 m.j. In the 

 high arctic districts the species is mostly found at a depth of 5 — 

 100 m., even at 2 — 3 m., less often at a depth of 100 — 220 m. or 

 still deeper.^) 



The specimen mentioned above from Barents Sea is the same, 

 which Danielssen & Koren describe as Myriotrochus brevis 

 (Huxley). Steenstrup, in his description of M. rinhii, had men- 

 tioned that it had stalked wheels; a little later Huxley, without 

 any knowledge of Steenstrup^s work, set up the species Chirodota 

 brevis with a diagnosis, which is generally well fitted to M. rinUi, 

 except that there was no mention of stalked wheels. On account 

 of this, some authors want to distinguish between a M. rinkii with 

 stalked wheels and a M. brevis with stalkless ones. Danielssen 

 & Koren presumed that they had both species in the collections 

 of the Norwegian North Atlantic Expedition. But their M. brevis 

 is nothing but a specimen of M. rinlåiy so strongly contracted that 

 the bodywall had burst and got very much thicker. Through the 

 thickening of the bodywall, the wheels have been made to lie rather 



1) Ludwig's statement (1900) about its presence even at a depth of 550 — 

 662 m. concern probably tlie next species. Among-st the districts mentioned 

 above there are some, Avhicli he outside of that which LuDWiG- (1900) mentions 

 viz. the Newfoundland Bank and the east j)art of the Siberian Sea. The ab- 

 sence of this species from Stuxberg's list (1880), which he wrote during the 

 „Vega" Expedition, is accounted for by his having called it Trodioderma elegans. 

 Théel who had an opportunity of revising the collections of this expedition, 

 corrects (1886 p. 38) this mistake, mentioning as regards Myriotrocims rinkii 

 specimens from „tlie Sea of Kara and the northern coast of Asia", Avhereas 

 regarding TrocJioåerma elegans he mentions „]Srova Zembla and the Sea of Kara" 

 as the only known districts. Thus Ludwig-s supposition (1900), that Myriotro- 

 chus rinkii could not be found on the North coast of Asia between 71^ E. and 

 1700 w.^ is wrong. 



