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









Iceland, 45 sps measured: 



- 



11. of shell 



5-C 



6—7 



8—9 



10-11 



12—13 



14—15 



16—17 



max. 19 (Raufarhofn) 



h. of apertiire 



4—5.4 



4.8—6.3 



6.3—78 



7.6—9.6 



9.2—11.2 



10.6—12.7 



12.2-14.1 



15.5 



br. of shell 



4.5—5.7 



5.4—6 8 



7.2—8.9 



8.7—11.3 



10.7—12.8 



124—14.2 



14—15.8 



17.5 ; 



br. of aperture 



2.7—3.7 



3.2—4.5 



4.1—56 



5—6.5 



6—7.4 



7—8.2 



7.8-8.1 



9.9 j 



lip to umbilicus 



1.6—2.2 



1.8—2.6 



2.4—3.3 



2.8—4.2 



33—4.5 



4—5 



4.4—5.5 



6.3 



lip to suture 



0.9—1.8 



1.1—2.1 



1.7-2.5 



2.2—3.5 



2.9—4.4 



3.7—5 



4.5—5 



6 



whorls 



about 4 



4 + 



4V4-4V2 



4V,-5 



5 



about 5 



5 + 



6 









West Grccnland, 35 sps measured: 





h. of sliell 



6—7 



8—9 



11—12 



14—15 



17—18 



20—21 



23—24 



max. 34 (Godhavn?) ' 



h. of aperture 



5—6.2 



6.4—7.9 



8.4—10.4 



11.2-13.3 



13.6—16.7 



15.9—18.2 



17.9—19.7 



25 



br. of sbell 



5.6—7.2 



7.5—9 



9.9—12.4 



12.9—15.8 



15.7—19 



18.4—21.3 



20.5—23 



32 



br. of aperture 



3.2-4.3 



4.3—5.4 



5.6—7 



7—9 



8.8—10.4 



10.5—11.7 



12.1—13.2 



18.2 



lip to umbilicus 



1.8-2.4 



2.3—3.2 



3.2—4 



4.2—5 



5.3—6.4 



6.3—7.5 



6.9—8.3 



10.7 



lip to suture 



1.1—2 



1.6—2.7 



2.5—3.8 



3.6—4.6 



4.6—6.2 



5.7—7.2 



6.5—8.1 



10.7 



whorls 



4 



4 + 



47,-5 



about 5 



5 + 



about öVj 



57,-6 



6 



The maximal size is attained by specimens from Behring Sea'(max. h. 45 — 60 mm). 

 Small specimens in all districts have as a rule a slightly projecting spire (distance from 

 lip to umbilical pad is greater than that from lip to suture along the lines of growth); 

 when the size increases the spire frequently becomes taller. Specimens showing a spire 

 of considerable height are the forma occlusa Wood 1848 (= elatior Middendorff 1849), 

 which represents only an extreme stage that is connected through all the traiisitions with 

 the forma typica. According to G. O. Särs (1878) this variety, at Finmark, is a litoral 

 form. In Ice Fiord I have found as a rule, from the collections of the Swedish expedition 

 of 1908, that in deeper water the spire grows higher and the aperture shorter, in shallow 

 water on the contrary the spire is somewhat shorter and the aperture larger; confer Pl. 

 4 Figs. 7 (St. 127, 25 m), 8 (St. 92, 85—45 m), 9 (St. 41, 234—254 m), 10 (St. 45, 70—42 

 m). On the western coast of Sweden higher specimens occur usually in deep water, 

 low-spired ones in shallower localities (cfr Pi. 4, Figs. 12, 13, 14), but it is not a rule that 

 they are strictly limited to separated bathy metrical zones, nor are they so within the 

 arctic districts in general. 



The whorls sometimes are considerably tumid, most in Greenland specimens (cfr 

 Fig. 1), and the Greenland shells are of ten more thick and ponderous than those from 

 Spitzbergen and eastern districts. Sometimes a feeble subsutural cordoii occurs as in 

 Lunatia groenlandica, but usually the lip is inserted angularly on the body whorl and it 

 is never concave (when seen from the spire). The umbilical callus is broadly rounded 

 and more or less clearly limited by a shallow furrow, which is never extended under 

 the callus (as in N. bathybii). 



Sculpture is usually absent, except fine lines of growth; but faint and very obscure 

 spiral lines (never sharp impressed strise) may occur in the smaller southern specimens 

 as well as in the larger arctic ones. 



