1902] The Holotliurioidea of Northern Norway. 23 



and Trochoderma elegcms. Of these the tvvo Molpadiidæ (Trochosioma 

 and Anl-yroderma) are to be met witli far to the south, down to 

 the 12° N., but only at great depths, where the water even within 

 the tropics is cold. On the coasts at a depth of less than 

 300 m., they are found exclusively within the region of the arctic 

 fauna. Chiridoia lævis has been found as far down as 67° 50' N., 

 the others have on the coast of Norway hitherto only been found 

 north of 69° 30' N. 



So as to give a true characteristic of the Holothurian fauna 

 of the north of Norway, I will compare it on the one hand with 

 that of the south of Norway, on the other with the high Arctic. 

 In doing so, one should, in the case of tlie Norwegian fauna, divide 

 the Holothurians "into two groups, according to- the different depths 

 at which they exist. Some are chief ly found at less depths 

 than 100 m., where the temperature is subject to rather great 

 variations according to the seasons; others again live exclusively 

 or preferably at depths of more than 100 m., where the variation 

 in the temperature of the water is small or almost none. 



The species which in the south of Norway are characteristic 

 of the greater depths, are, as a rule, also to be found north of the 

 Arctic circle: Stichojms tremidus, Bathyplotes natans, Mesothuria 

 intestinalis, Cucumaria hisjjida, Fsoliis squamatus (?), Lahidoplax 

 husM^) and Myriotroclius vitreus. In the south of Norway there 

 are also the four following species : Stichojms griegi Ostbbgr., Ba- 

 thyiolotes tizardi (Théel), B. fallax Osterge. and Thyone sevrifera 

 OsTEEGR.') Amongst these Stichoijus griegi, Bathyplotes tizardÅ 

 and B. fallax are hitherto found only in the vicinity of Bergen (60° — 

 62° N.). They are now all of them know^n in numerous specimens. 

 Even Thyone sevrifera is found only within a small district, the 

 Trondhjem Fiord, where it can be got in rather great numbers 

 together with Cucumaria hisjjida. These four species are thus 

 spread over very small districts. All those which in southern 

 Norway have wider distribution in the greater depths, are also to 

 be found north of the Arctic circle. 



1) This species is often found at a rather small depth. Lahidoplax Imfilxi 

 could therefore almost as well be comited to the species, which as a rule live 

 in less depths. Even Sticlwpns tremulus and Mesothuria intestinalis are not so 

 rarely met with a a less depth than 100 m. 



-) The latter by me (1898 a) described species has been overlooked by 

 LumviG (1900). 



