10 NILS ODHNER, NORTHERN AND ARCTIC INVERTEBRATES. III. OPISTHOBRANCHIA ETC. 



Synopsis of Genera and Species. 

 Fam. Actaeonidse. 



Actseon Montport 1810. 



Shell spiral] y striated; whorls 7 — 8; cohimella with a prominent fold; colour 

 reddish or violet, often with 3 wliite spiral girdles. The cephalic disc reflexible över 

 the anterior part of the shell. L. about 17 mm. A. tornatilis (Linné 1766). 



Shell pelhxcid, greenish and more shining than in the type, with 4 whorls 

 and yellow spiral bands. L. 3,8 mm. var. tenellus Loven 1846. 



Fam. Tornatinidse. 



I. Shell cylindrical or conical; spire obtuse Retusa Brown. 



II. Shell contracted at both ends; spire acuminated Volvula Adams. 



Retusca Brown 1827. 

 Utriculus Brown 1844.^ 

 I. Spire concealed. 



A. Apex abriiptly truncated. 



1. The last Avhorl not tapering from the middle upwards; no spiral striee; 

 outer lip projecting beyond the apex; shell constricted in the middle; 

 colour white. L. 4 mm. R. truncatnla (Bruguiére 1792). 

 Shell more transparent, nearly cylindrical, not constricted in the middle. 

 L. 5 mm. var. pellucida (Brown 1827), 



2. The last Avhorl tapering backwards, abruptly conical : spiral striee in- 

 distinct ; outer lip projecting beyond the apex and furnished with a sharp 

 keel surrounding the sunken apex. L. 8 mm. R. ovata (Jeffreys 1870) 



= conulus (Deshayes) in G. O. Särs 1878. 



B. Apex obtusely rounded. 



1. Shell umbilicated and spirally striated; columella folded. 

 a. The breadth of the shell = the half length. 



+ . Apex deeply and widely perforated; colour white. L. 4 mm. 



R. umbilicata (Montagu 1803). 

 + +. Apical perf oration smaller; columellar fold and strise very distinct; 

 colour white, epidermis broAvn. L. 2 mm. 



R. strigella (Loven 1846). 



h. The breadth = ''/* of tlie length; shell with a few eoarse spiral ridges and microseopical strise. 

 L. 2,n mm. R. substriata (Jeffreys 1877). 



Tlio iiaiiic rtriculiis was employcfl by ScmtM.\cHEE in 1H17 for a l'rosnbran('li. 



