KUNGL. SV. VET. AKADEMIENS HANDUNGAR. BAND 63. N:0 2. 23 



and measures about 85 mm. in length. The length of the specimens from Spitzbergen 

 do not exceed 45 mm., and the single specimen from the Swedish coast measures 

 22 mm. Off Spitzbergen, in Stor Fjord, gigantic individuals have been dredged, 

 measuring 137 mm. in preserved state (Redikorzew 1906, p. 132). Like the specimen 

 from the Swedish coast those from the Norwegian coasts are of small a size; Bjerkan 

 has stated that, in a collection from Finmarken, the largest specimen did not exceed 

 32 mm. in length. 



Pelonaia corrugata occurs in the Artic and Boreal regions and is widely distri- 

 buted in both. It is generally maintained that it is an Arctic form which has wan- 

 dered southward. In the Arctic region this species attains its largest size, but it 

 ought to be observed that specimens from the Boreoarcic mixture zone almost equal 

 the first-mentioned ones, individuals measuring at least 110 mm. having been collected 

 on the east coast of Iceland. 



As appears from the above, P. corrugata inhabits the fjords of northen 

 Norway, but has also been found along the west and south coasts of this country. 

 Its occurrence in the last-mentioned localities has been explained by the theory 

 of an Arctic relic fauna living in those fjords (Särs 1866). J. A. Grieg who 

 has investigated the matter in låter time and published the results of those in- 

 vestiagtions as recently as the year 1913, has accepted the same view that Pelo- 

 naia corrugata is a relic form: »De fleste arter kan dock ikke betragtes som 

 'arktiske utliggere' da de har forstaat at tillempe sig efter de forandrede livsvilkaar. 

 — Der er dog nogen arter hos hvem öiensynlig denne evne har vaeret litet utviklet. 

 De optraer spredt og faatallige og meget ofte kun i forkröblede eksemplarer. Av 

 saadanne arter kan naevnes Pelonaia corrugata. — Disse arter kan derfor med rette 

 betragtes som relikter. Det er sandsynlig at det arktiske element i fjordfaunen 

 stämmer fra istiden» (1. c. p. 30). This view of Grieg does not, however, seem to be 

 supported by what is known about the distribution of this species. P. corrugata is not 

 an exclusively Arctic form, on the contrary, it has been collected in the eastern Boreal 

 region in several localities: off the Brittish coasts in many places, in the North Sea 

 between Borkum and Helgoland, off the coasts of Denmark east of Hjelmen, between 

 Anholt and Kullen in Cattegat, and, as has been mentioned above, off the Swedish 

 coast in Gullmarn. And if we consider the numerous localities and especially the 

 depth in which P. corrugata has been dredged on the west and south coasts of Nor- 

 way the theory that this species belongs to the relic fauna does not become more 

 probable. In Hardangerfjord it has been collected at Saetveit, depth 10 — 50 m, only 

 one specimen, at Arendal in a depth of 24 m, in Christianiafjord it has been found 

 in the mouth, at Bollaerene, in a depth of about 20 — 30 m. Thus the local con- 

 ditions do not appear in any way remarkable. Why may we not then suppose that 

 the presence of this species in the last-mentioned localities is due to the same pow- 

 ers which brought it to other places in the Boreal region? Judging from the 

 facts mentioned above, this supposition is no doubt closer at hand. The occurrence 

 of P. corrugata in Gullmarfjorden on the Swedish west coast is probably purely ac- 

 cidental; only a single specimen has been collected at a depth of 10— 15 f ms off the 



