16 NILS ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. V. PROSOBRANCHIA. 1 DIOTOCARDIA. 



B, Lateral teeth of the radula 4 on each side; whorls slightly convex with 3 — 

 4 spiral ribs of uniform strength; colour pearl-white; animal differing from 

 all Trocliidee by 4 lateral cirri on each side (instead of 3). H. 10—14 mm 



C. occidentale (Mighels & Adams 1841). 



PI. 3 figs. 24 -25. 



Craspedotus Philippi 1847. 

 Danilia Brusina 1865. 



Sljell elevated, inipeiforate; spiral cords 3 — 4 on tlie upper, 9 on tlie last whorl. II. 7 — 8, D. (i — 7 

 mm (France, Locakp 1892) C. otavianus (Cantraine 1835) 



(= Monodonta Tinei C^alcaka 1839). 



Margarita Leach 1819. 



I. Radula with a rudimentary lateral tooth; lamellae denticulated in the inner and 

 the outer margin. 



A. Shell smooth, without sculpture (except extremely fine spiral lines on the 

 base), depressed conical; umbilicus narrow, not surrounded by a carina; 

 aperture twice the spire in height; colour grayish green or reddish brown; 

 radula . 1 . (6 . 1 . 6) . 1 . oo, the central cusp of the median tooth < their 

 lateral denticles; height of the last whorl above the columella, seen from 

 aperture, half its breadth. H. circa 4—9; D. circa 5—11 mm 



M. helicina Phipps 1774. 



PI. 3 figs. 26—34; PI. 6 figs. 3—5. 



B. Shell with spiral sculpture (sometimes absent in M. groenlandica). 



1. Sculpture consisting of very fine and dense spiral striae; umbilicus 

 narrow; colour light yellowish or greenish, sometimes dark bluish, often 

 vividly iridescent. Spire usually elevated, longitudinal sculpture (lines 

 of giowth) feebler than the spiral one; shell shining. Radula oo . 1 . 

 (5 . 1 . 5) . 1 . 00. H. 6—10, D. 6—11 mm M. oHvacea (Brown 1827) 



(= M. argen tata Gould 1841). 



PI. 3 figs. 41—46: PI. 4 figs. 1—3; PI. 6 figs. 8—10. 

 Spire usually more depressed; longitudinal sculpture of very fine 

 dense-set lamella? of about the same strength as the spiral lines, 

 which are fainter than in the type; shell of a light colour, not 

 shining; radula oo . 1 . (4 . 1 . 4) . 1 . oo var. gigantea Leche 1878. 



PI. 3 fig. 44; PI. 4 figs. 2—3; PI. 6 figs. 11 — 13. 



2. Sculpture consisting of coarse and sparse ridges or of sparse impressed 

 limes (sometimes absent); umbilicus usually wide; shell often not irides- 

 cent. 



a. No prominent longitudinal sculpture, though irregular striae or folds 

 sometimes are present at the suture ; spiral ribs or striae mostly 

 present, seldom wanting; usually no keel around the umbilicus; 

 height of the last whorl, above the columella, seen from aperture. 



4 



