CRUSTACEA MALACOSTRACA. IV. 59 



52. Diastylis polaris G. O. Sars. 



1872. Diastylis polaris G. O. Sars, Ofv. Kgl. Sv. Vet.-Akad. Forh. Arg. 38, p. 797. 



1872. stygia G. O. Sars, 1. c. p. 798. 



1873. polaris G. O. Sars, Kgl. Sv. Vet.-Akad. Handl. Ny Foljd, Bd. 11, 110. 6, p. 4, Tali. I, Fig. 



1-3- 

 1873. stygia G. O. Sars, 1. c. p. b, Tali. II, Fig. 4—7. 



1887. G. O. Sars, Challenger Rep. Vol. XIX, II, p. 44, Pis. VI— VIII. 



1901. polaris Ohlin, Bihang K. Sv. Vet.-Akad. Handl. Bd. 20, IV, no. 12, p. 50. 



[913. stygius and polaris, Stebbing, Das Tierreich, 39. Fief. p. 100. 



More than a year before Ohlin cancelled/), stygia as a synonym to I), polaris I had arrived at the same 

 result while determining the "Ingolf" material, viz. the specimens from Stat. 25 in the warm area and from 

 the stations in the cold area. I found that two or three oblique rugae were always more or less developed on 

 the carapace, which is a character for D. polaris, while in females without marsupium and in immature males 

 (adult males are unknown) each of the three anterior free thoracic segments has in the median ventral line 

 a more or less developed denticle, and many, but not all, specimens have an erect, fine, spiniform denticle 

 above on the last thoracic segment, but both these features are according to Sars (in 1872) characters for 

 D. stygia. From Stat. 36 (1435 fath., in the warm area) three young specimens with the last pair of legs still 

 wanting were put aside for future study ; these specimens are proportionately large, the largest measuring 

 8 mm. in length, while specimens without last pair of legs from the cold area or from 582 fath. in the warm 

 area are only about 5.8 mm long. When in 1919 the present paper was worked out, the material was again 

 examined; I found that the young specimens from Stat. 36 have no vestige of oblique rugae on the carapace 

 and agree on the whole well with Sars' first description of D. stygia, excepting in possessing not a single spine 

 but two spines in the median dorsal line of last thoracic segment, the first spine larger than the second, and 

 Sars describes two such spines in his "Challenger" specimens. According to Sars first pair of legs are shorter 

 in D. stygia than in I), polaris, and in the three specimens without rugae the carpus of these legs is rather far 

 from reaching the end of pseudorostrum — but in young specimens from the cold area with ruga- but still 

 without last pair of legs, first legs show the same feature, because they are proportionately shorter in such 

 young than in subadult or adult specimens. — The result is that I must consider absence of rugae in the young 

 specimens from Stat. 36 as mere variation, that I>. polaris and D. stygia are the same species, which shows some 

 variation, partly individual, partly according to localities. If D. stygia shall be kept as a separate form, the 

 only character hitherto observed seems to be the absence of ruga? on the carapace — and of the "Ingolf" 

 material only the specimens from Stat. 36 have no rugae. 



It may be mentioned that the Fpicarid Cumoechus iiisi^uis H. J. H. was found in the marsupium 

 of specimens from the "Ingolf" Stat. 113 and 138. 



Occurrence. Taken by the "Ingolf" at 12 stations. 



Davis Strait: Stat. 25: Fat. 63°3o' N., Fong. 54 25' \Y., 5.S2 lath., temp. 3.3 ; i(> specimens, the 



major part mutilated and young. 



