14 N. ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. VI. PROSOBRANCHIA. 2 SEMIRROBOSCIDIFERA. 



Limits of Formål Variation (100 sps measured): 



L. 



8—9 



9—10 



10—11 



11—12 



12—13 



max 12.9 (Gullmarn) 



Br. 



about 6 — 7.3 



6.3—8.2 



7—8.8 



7.8— about 9.5 



9—10.3 



10.2 



H 



» 4.7—5.7 



5.1—6.4 



5.6—7 



6.5—7.7 



7.2—8.4 



8.3 



Variation of sciilpture and colour: The sculpture usnally consists of strong trans- 

 verse costse (Figs, 36, 37), but these may be fainter (Figs. 38, 39) or absent from the dorsal 

 though never entirely from the ventral side of the shell (Fig. 40). When the costee are 

 strong, they conceal the spire, which forms at most a shghtly projecting knöt; with 

 fainter costse it shines through and in small shells it projects freely. On the under side 

 of the shell costae always appear (though sometimes feeble), even when the dorsal side 

 is wholly devoid of them. — On the Scandinavian coasts the colour of the shell is whitish 

 with a yellowish or reddish tint, usually with some obscure central and terminal orange 

 clouds on the back. The smooth shells have a half hyaline milky colour. 



Variation of the radula: Specimens from Gullmarn have a broad median tooth 

 with a strong and pointed central cusp and many smaller, more or less irregular-sized 

 denticles on each side of it; the lateral teeth are denticulated in their outer margin and 

 with one denticle in the inner edge; the uncini are smooth. Owing to the strong central 

 cusp of the median tooth the radula differs somewhat from that figured by G. O. Särs 

 1878 (Tab. V, fig. 8). 



General Distribution: 



Norway: Lofoten, 1 sh. (G. O. Särs 1878) to Trondhjem, dead, 30 fms (M' Andrew 

 1856); Vigten Islands to 20 fms (M'Andrew 1857); Christiansund (Lilljeborg 1852*); 

 Bergen, rare (Friele 1874); Haugesund, 5 — 20 fms (Metzger 1875); Christiania Fiord, rare 

 (Asbjörnsen 1854), 20—50 fms (G. O. Särs 1878). — Bohuslän: Väderöarna, 35—100 

 fms; Gullmarn, Flatholmsrännan, 25 — 35 fms, and Löken, 22 fms (Malm 1855, Théel 

 1907). — Faroe Islands, cast upon shore (1. 13 mm; Mörch 1868); N. of Hebrides, 189 — 

 530 fms (Jeffreys 1869). — All British coasts (Jeffreys 1867; Nichols 1900). — Dogger 

 Bank (Hargreaves 1910). — North Sea coast of Holland and Belgium, rare (Maitland 

 1897). — France, common, down to 250 m (Locard 1892, 1899). — Portugal, common 

 (Nobre 1905). — Spain and Mediterranean to Aegean (Carus 1890). Depths 5 — 530 

 fms. Gravel, shells, corals. 



Natica clausa Broderip & Sowerby 1829. 



Pl. 3, Figs. 1 — 8, 5—14, 16, 17; Pl. 5, Figs. 7—14. 

 Habitat: 



West coast of Sweden: Gullmarn (Zool. St.), 2 sps, max. h. 9.2; ap. h. 7.0; br. 9.4; 

 ap. br. 5.2; iimb. 2.8; sut. 2.i; wh. 4 V, (fig. 14). — Koster, 10 — 15 fms, rocks (1863), 1 

 sp., h. 8.o; ap. h. 7; br. 8.2; ap. br. 4.»; amb. 2.g; sut. 2.2; wh. 4 V4 (fig- 13); D:o, 100 fms 



