38 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. PROSOBRANCHIA. 2 SEMIPROBOSCIDIFERA. 



The coloiir of tlie shell is always uniformly yellowish white (Swedish coast and 

 East Greenland [Natica horealis Gray 1839]), brownish or greenisli without bands; 

 at the suture, however, a darker brownisli diffiise coloration is usually present. 



In specimens from Siberia and Behring Sea tlie insertion of tlie lip is somewhat 

 less characteristic tlian usual; it is less produced and less concave, thus causing a very 

 obtuse angle witli the body-whorl, tliough it is not so well marked as in L. tenuistriata. 



The blunt sub-sutural keel is sometimes absent (and of ten so in southern forms). 

 In one shell from Hinlopen it causes a funnel-shaped sutm-e, owing to which the shell, 

 wliich is elongated, reminds one of Amauropsis, biit the insertion of the lip and the 

 smooth cuticula show that it belongs to L. pallida. 



Sometimes a faint sculpture of indistinct lines of irregular strength occurs, which 

 may be more or less conspicuous, but is never composed of impressed strise as in L. te- 

 nnistriata. Krause (1885) has observed it in specimens from Behring Sea, more con- 

 spicuous in larger than in smaller shells. 



The thickness of the shell is subject to some variation, as the Scandinavian, the 

 Iceland and generally the Greenland shells are thicker and more ponderous than those 

 from Spitzbergen. In Behring Sea the shells are of moderate solidity. One specimen 

 from Vega Station 1072 is remarkable, as it has the umbilicus entirely closed by a cal- 

 lous pad like Natica clausa; the operculum is, however, corneous and the radula typical. 



Variation of the Radula. 



A reduction of size of the radula similar to that shownto occur in Natica clausa, 

 where the deep water and dwarfed forms usually have a narrow radula, is not to be ob- 

 served in such a large degree in L. pallida. The radida however, is often, tliough not 

 universally, somewhat narrower in breadth in specimens living in deep water and some- 

 what narrower in forms from southern than in those from arctic districts, as is evident 

 from the following table (dimensions in millimetres): 



1 



D i m n s 



i o n 



s of 



t h 



e s 11 



e 1 1 



h. 



ap. 1). 



br. 



ap. br. 



unili. 



sut. 



wh. 



12.7 



•J.G 



Il.l 



6.1 



4.3 



37 



47. 



11.3 



9.1 



10.3 



5.8 



3.7 



3 



4 + 



10.4 



8.6 



9.3 



5.4 



37 



2.5 



4 + 



10.2 



8.4 



9.2 



53 



3.5 



2.2 



4V. 



13.8 



11.8 



12.8 



7.3 



5.5 



2.8 



4^/4 



16.5 



13.3 



15 



8.6 



6.8 



4.3 



47= 



14 



11.5 



12.2 



7 



5.1 



4.2 



474 



12.5 



9.3 



11 



6.4 



4.2 



3.2 



4 



13.5 



10.3 



12.1 



7 



4.8 



4.2 



— 



9.3 



7.5 



8.1 



4.6 



3.4 



2.2 



4 + 



10.9 



8.9 



9.8 



5.5 



4.2 



2.3 



47. 



18.4 



13.8 



15.7 



8.8 



6 



5.7 



5 + 



10.7 



9.2 



10 



6 



4.2 



2.7 



473 



Broadth of 

 the radula 



Ice Fiord (1908;, St,. 41, 234—254 m (Pl. 3, Fig, 29) 



» >. » st. 94, 147—141 m 



» St. 92, 85—45 m (Pl. 3, Fig. 28) . 



» » St. 127, 25 m 



» » » » >> » » (Pl. 3, Fig. 27) . . . 



Mossol Bay, 9 fms • . . . . 



N. E. of Tho Seven Islands, 150 m 



East Greenland, 3—10 ni (IM. 4, Fig. 8) 



West Greenland, 9 — 36 fnis 



Berufjord, Iceland, 40 fms 



Knäholmen, Öresund 



Kullen — Hallands Väderö, 14 — 15 fms 



Gullmarn (cfr Pl. 4, Fig. 5) 



O 22 

 0.22 

 0.21 

 0.22 

 0.36 

 0.33 

 0.30 

 0.32 

 0.31 

 0.20 

 O 23 

 0.33 

 0.22 



