56 NILS ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. V. PROSOBRANCHIA. 1 DIOTOCARDIA. 
Variation of the radula: Two forms of radul&e are distinguishable (cfr Pl. 6, 
figs. 8—13): the one with 11 median teeth (5.1.5), the other with 9 (4.1.4). The 
form of the teeth is somewhat different in these cases, having in the first a broad 
semicircular base, attached with a broad (not lengthened) area; the apices are fur- 
nished with long central cusps and feeble denticles on the sides. In the other case 
the teeth are somewhat quadrangularly rounded and more contracted beneath the 
apices, with narrower and more lengthened feet. The denticulation is more marked 
and extends usually far towards the central cusps; these are usually small, but so- 
metimes rather prominent (e. g. specimens from Cloven Cliff, fig. 9). The first- 
named form of radula is characteristic of var. gigantea and is only met with in spe- 
cimens of its sculpture (from Horn Sound, Matotschkin sharr and Behring Sea). Auri-: 
villius (1887) describes the specimens from Behring Sea as the typical form, but they 
have the shell and radula characters of var. gigantea LECHE, and the var. gigantea 
of Aurivillius is the typical form; of the first, one specimen has 11 median teeth 
(according to Aurivillius), thus presenting mixed typical and varietal characters. — 
The number of lamell&e varies from about 20 to 25 (both in type and variety), but 
sometimes amounts to about 60 (var. gigantea, Cloven Cliff). 
General Distribution: 
Norway: Vardö to Lofoten (d. 3.5, G. O. Sars 1878; h. 5, Schneider 1885, 
1891); Tromsö (Schneider 1881); Bogfjord (Norman 1902). — Murman coast, White 
Sea and Arctic Ocean N. of Siberia (Herzenstein 1893). — Kara Sea, 2—90 fms (Col- 
lin 1887; Leche 1878 + var. gigantea). — Barent Sea, 80—211 m (Knipowitsch 19012). 
— Nova Zembla (Dautzenberg 1911). — Siberia; Behring Sea, 3—55 fms (Aurivillius 
1887, + var. gigantea, cfr above; Dall 1875; Crosse 1877; Krause 1885). — Iceland 
(Odhner 1910). — Scotland (Jeffreys 1869). — East Greenland, 3—220 m (Hägg 1905). 
— West Greenland, to 200 fms (Posselt & Jensen 1899). — Grinnel Land (Smith 
1877). — Jones Sound and North Devon, 4—40 m, max. d. 7.5 (Grieg 1909). — 
Parry Islands (Sutherland 1852). — East Canada, 20—60 fms (Whiteaves 1901). — 
New England (d. 4, Gould & Binney 1870). Depths to 200 fms. Clay, sand, stones, 
alge. 
Margarita groenlandica (CHEMNITZ 1781). 
Pl. 4 figs. 4—27; Pl. 6 figs. 14—-20. 
Habitat: ! 
West coast of Sweden: Gullmarn (Lovén) 1 sp., together with Moelleria costu- 
lata and Rissoa Jeffreysi; d. 2. — Kosterfjorden, 10—15 fms, rocks (Aug. 1863) 
3 sps, white, feebly sculptured or smooth, max. h. 4.5; ap. 3; d. 6; wh. 4'/2 (var. 
2a—2 c). 
1 The notes in brackets after the measurements refer to the account of the variation given below. 
