KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 50. NIO 5. 



37 



the same maximum as has beeii fouiid for Greenland specimens; it grows smallest in 

 Iceland (max. h. 14,4 mm). The following table gives data of tlie increase of the shell 

 and of its size in relation to the whorls in the same manner as was given above for Natica 

 clausa: 



N u m b e r of whorls: 



Height of the shell from 



West coast of Svveden 



Tromsö 



Treurenburg Bay 



Vega St. 1068 



Berufjord 



West Greenland (low and high-spired forms) 



2 7. 



3 



3 7. 



4 



4 7. 



5 



5 7. 





3.8 



6 



8 



14.3 



17—18.5 





— 



about 3.5 



6 



8—10 



14 



18-19 



— 



— 



4.2 



62 



8.7 



16 



24 



36.5 



— 



4.3 



7 



— 



16.5 



23.5 



37 



2.3 



— 



5 



8 



11 



— 



— 



2.6 



35 



5 



7.3 



1 10—11 

 t 12—13 



about 15 

 about 17 



— 



From this table it is evident that the maximal size of specimens from Behring Sea 

 and Treurenburg Bay is in the first place due to the higher number of whorls (5 V2), com- 

 pared with that in other districts (at most 5). But if we leave this fact oub of account, 

 it is obvious that specimens with the same number of whorls here are larger than in 

 other districts. In this case there exists a striking resemblance to Natica clausa. But 

 the two species exhibit a considerable difference in south Scandinavian waters, where 

 Natica becomes dwarfed and much smaller than in Iceland and Greenland, wliile 

 L. pallida shows scarcely any reduction in size compared with arctic districts, even 

 surpassing the Iceland form. 



Of L. pallida, as of N. clausa, two extreme forms are distinguishable, the one higher 

 with comparatively shorter aperture and large distance from insertion of lip to siiture, 

 the other more depressed with a larger aperture and a sliort corresponding distance. 

 These extreme forms seem to be in the same relation to each other as was stated to be 

 the case for N. clausa, viz. that the higher form usually inhabits deeper water (but 

 sometimes also occurs in slight depths e. g. E. Greenland). In the Ice Fiord this is also 

 the case (confer Pl. 3, Fig. 27, St. 127, 25 m; Fig. 28, St. 92, 85—45 m and Fig. 29, St. 41, 

 234 — 254 m), and 011 the Avest coast of Sweden specimens from deeper water grow higher 

 than shallow water shells (cfr Pl. 4, Figs. 4, 5). Numbers of transitions occur, however, 

 between these extreme stages. In contrast to N. clausa, L. pallida has not given origin 

 to any distinct deep-sea form. 



AuRiviLLius (1887) and Friele & Grieg (1901) consider Lunatia pallida Bröd. 

 & Sow. and L. groeiilandica Beck sejiarate from each other. The last-mentioned au- 

 thors state as a reason for their opinion (pag. 69), that »Natica pallida differs greatly 

 from groenlandica in its comparatively greater length, and its more elongated aperture», 

 but, according to the above statements, these characters are not fixed but are subject 

 to a considerable variation, and the forms belong consequently to the same species, for 

 which the iiame L. pallida may be reserved. This opinion has also been expressed by 

 Dautzenberg & FiscHER 1912 (pag. 237). 



