14 NILS ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. HI. OFISTHOBRANCHIA ETC. 



2. Umbilicus partially closed ; outer lip strongly sinous, much produced above. 

 L. c. 2,5 mm. Shell horn-coloured D. hiemalis (Couthouy 1839). 



B. Shell pellucid with close, impressed spiral strige; outer lip sharply angulated 

 at the top, sinuous ; aperture not dilated. L. 6 mm. Radula similar to that 

 of a Philine, with denticulated laterals D. densistriata (Leche 1878). 



Fam. Aceridae. 



Acera Müller 1776. 



Stomach-plates 12 — 14; cephalic disc long, narrow; animal not perfectly re- 

 tractile into the shell. 



Shell with microscopical striae; spire flattened, surrounded by a sharp keel; 



cuticula pale brown. Whorls 3 — 4. Colour of the animal brownish. L. 50 mm, 



animal; 14 mm, shell A. bullata Müller 1776. 



PL. II figs. 1—3. 



Fam. Philinidae. 



Philine Ascanius 1772. 



Cephalic disc very large; parapodia erected, swollen; mantle covering the shell 

 wholly and produced beyond it behind ; shell vitreous or opaque. 

 I. Stomach-plates distinct, calcareous. 



A. Radula without uncini, 1.0.1; shell broadly oval. 



1. Spiral sculpture none; outer lip reaching up above the apex, and 



a. arcuated above; shell subpellucid; aperture uniformly rounded below. L. 

 45 mm, animal: 15 — 20 mm, shell 



Ph. aperta (Linne 1766) = quadripartita Ascanius 1772. 



PL III fig. l. 



b. forming a right angle above; shell vitreous, aperture obliquely expanded. L. 3 mm, shell 



Ph. vitrea M. Saks 1870 = infortunata Pilsbkv 1895. 



2. Shell with spiral sculpture. 



a. Spiral striae close, fine and undulating, outer lip depressed above, not ex- 

 tended beyond the apex. 



+ . Laterals of the radula serrated in the margin. 



a. Shell elongated, much contracted above, broadest below the middle; 

 last whorl only a little convex; suture terminating in a slit; sculp- 

 ture microscopical. Head, without median furrow, > the mantle. 

 L. 9—12 mm, shell Ph. Ossian-Sarsi Friele 1877. 



ß. Shell very broad, oval; the last whorl strongly convex; no slit at 

 the suture. Apex and the superior lobe of the aperture obliquely 

 truncated. Head-lobe the mantle, white. L. 18 mm, animal; 7 

 mm, shell Ph. finmarchica M. Sars 1858, 



