KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 48. N:0 1. 



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Sculptural variation: The sculpture of S. obscura is highly varied, but no dis- 

 tinct characters can be found by which the forms are separated from each other. 

 Transitional stages occur between most of the forms. The typical form has usually 

 an umbilical keel, but one specimen from the White Sea is destitute of it and thus is 

 a transition form to var. bella. On the other hand there are specimens of the latter 

 variety, furnished with umbilical cords (off Ice Fiord). Var. multilirata (Greenland) 

 has a greater number of revolving ridges, more or less prominent, thus forming a 

 transition stage to var. islandica with spiral grooves, but without keels. The strongest 

 sculptured specimens from Greenland show relationship, on the other hand, to var. 

 bella. Transition forms between the type, var. albula and var. intermedia occur at 

 Murman Coast and the Kola Peninsula. As to form, however, extreme varieties differ 

 a good deal from each other, e. g. var. bella, Norway, and the typical var. multi- 

 lirata, Greenland. 



Variation of the radida: The number of lamellae amounts to 10 in var. intermedia 

 and albula (from Kola — Behring Sea), but small specimens (d. 3.2 — 4) of the same variety 

 and from the same localities have only 6 lamellae on each side. In specimens of var. multi- 

 lirata from Davis Strait, 8 lamellae occur, but young specimens (d. 3.2) have only 6 ; the 

 same number is found in var. bella from Grötsund. 7 lamellae are found in the spe- 

 cimens from the White Sea, which mark a transition from the type to var. bella; 

 6 lamellae are found in the majority of specimens of var. bella (from Godthaab and 

 72° 10' N.), in var. albula (Kildin Island) and in var. finmarchica (Finmark; young 

 specimen of 3.8 mm diameter). One large specimen from Umanak was investigated; 

 it had only 5 lamellae on each side. From these statements it is obvious that the 

 variation in the number of lamellae is not entirely dependent upon the growth in the 

 present species, as in forms of Margarita. Moreover one qualitative character of the 

 lamellae is subject to variation, namely their denticulation. Usually only the rha- 

 chian and median teeth have denticulated margins, but the denticulation is sometimes 

 found more or less extended to the lamellae, the first ones (Godthaab, Umanak) or 

 nearly all (Davis Strait) being bilaterally serrated. Young specimens seem to have 

 traces of a few denticles on both sides of every lamella (Matotschkin sharr; Vega 

 Exp.) even when adult specimens of the same form have them entirely smooth. The 

 rhachian tooth has a greater or less number of denticles (10 — 5) on each side and 

 is somewhat varied in form (cfr Figs. 9—20). 



General Distribution: 



Norway: var. finmarchica, Vardö — Lofoten, 120- 300 fms (d. 5; G. 0. Sars 1878; 

 Schneider 1891); var. bella, Vadsö— Lofoten, 30—40 fms (d. 7, G. 0. Sars 1878; 

 Schneider 1881, 1885, 1891; De Guerne 1886); Bogfjord (Norman 1902); var. alhula, 

 Vadsö— Magerö, 10-25 fms (d. 10, G. 0. Sars 1878; De Guerne 1886; Schneider 

 1894; Norman 1902). — Murman Coast, Nova Zembla, Arctic Ocean N. of Siberia, type 

 and var. alhula (Herzenstein 1893). — Barent Sea, 275—308 m, type (Knipowitsch 

 190L'). — Kolguev, 20 fms, var. alhula (Melvill & Standen 1900). — Kara Sea, 2— 



K. Sv. Vet. Akad. Handl. Bnnd 48. N:o 1. 10 



