18 NILS ODHNER, ^'ORTHERN AND ARCTIC INVERTEBRATES. V. PROSOBRANCHIA. 1 DIOTOCARDIA. 



II. Sculpture consisting of longitudinal folds and very fine spiral striae, more dis- 

 tinct on the base; 1 — 3 umbilical keels present; shell conical, vv^hitish, greenish 

 or brownish. H. 8—11; D. 9—12 mm. Radula 11— 12 . 1 . (3 . 1 . 3) . 1 . 11-12 



S. varicosa (Mighels & Adams 1842) 

 (= Margarita elegantissima S. Wood 1848). 



PI. 5 figs. 6—14; ri. 7 figs. 5 — 6. 



III. Sculpture consisting of spiral keels, which are usually more prominent than 

 the longitudinal folds or strise; colour whitish, greenish or brownish. Radula 

 5—10 . 1 . (2 . 1 . 2) . 1 . 5—10. Type with 1 — 2 prominent spiral ridges and fine 

 Striae; umbilical keel present. H. circa 7, D. 8 mm 



S. obscura (Couthouy 1839). ^ 



PI. 5 fig. 22; PL 7 figs. 9—20. 



(Specimens with 3 strong spiral ridges and a feeble umbilical keel pass over 

 into var. finmarchica.) 



a. Spiral ridges many, strong, though 2 — 3 are more prominent than the rest; 

 umbilical keel present var. cineraeformis Leche 1878. 



b. Spiral ridges many, of about uniform strength; umbilical keel present 



var. albula Gould 1862. 



PI. 5 fig. 20. 



(Specimens without umbilical keel pass over into var. bella.) 



c. Spiral ridges replaced by fine and dense striae; umbilical keel present 



var. intermedia Leche 1878. 



PI. 5 fig. 23. 



d. Spiral ridges 4 — 5, unequal in strength; fine longitudinal striae; no umbi- 

 lical keel; H. 4.5; D. 5 mm var. finmarchica n. n. 



(=Machaeroplax obscura Couth, of Sars 1878). 



PI. t) figs. 36—35. 



e. Spiral ridges about 7, unequal in strength; longitudinal striae indistinct; 

 no umbilical keel; H. 4.8; D. 6.4 mm var. multilirata n. var. 



PI. 5 figs. 28—30. 



f. Spiral lirae undeveloped, replaced by finer striae, about 6 — 8 on the last 

 whorl; no umbilical keel. H. 4.5, D. 5.8 mm var. islandica Odhner 1910. 



PI. 5 fig. 24. 



g. Longitudinal sculpture coarse and distant, often of nearly the same strength 

 as the spiral one; this consisting of a few equally strong ridges; umbilical 

 keel present or not. Radula with 5^ — 8 lamellae on each side. H. 6.5, D. 

 7 mm var. bella (Verkrüzen 1875) G. O. Sars 1878. 



PI. 5 figs. 25—27, 31, 34. 



IV. Sculpture consisting of spiral riblets and rows of tubercles (surface of the shell 

 nodulous or granular). 



A. 3 prominent spiral ridges on the last Avhorl and 1 on the base, surrounding 

 the umbilicus; aperture roundish; colour pearl-white. H. 8, D. 7 mm. 

 Radula 5 . 1 . (3 . 1 . 3) . 1 . 5 (Friele 1877) S. cincta (Philippi 1836) 



(= Trochus amabilis Jeffreys 1865). 



