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



II. Stomach without plates; foot forked behind, with small parapodia; shell thin, 

 transparent, globose: spire concealed or prominent: animal retractile into the 

 shell ; radula 1.1.1, the laterals crossing the laminae mediee Diaphana Brown. 



Ncapliaiider Montfort 1810. 

 I. Spiral stria3 deeply impressed, in the bottom with fine punctures; outer lip in 

 the middle almost straight, ronnded above and, seen from the top, bowed in S- 

 form with a wide concavity near the apex, which is sunken and surrounded by 

 a keel. Cuticnla yellowish. L. unto 28 mm. S. lignarius (Linné 1766). 



II. Spiral punctures very distinct; outer lip slightly bowed, angled above and, seen 

 from the top, convex up to the apical insertion; apex without keel, not sunken; 

 shell in the middle broader, the aperture less dilated below. Cuticula yellow or 

 brown. L. about 35 mm. 



S. punctostriatus (Mighels 1841) = librarius Loven 1846. 



Atys Montfort 1810. 

 The spiral strise less distinct in the middle of the shell; outer lip extended 

 above the apex which is furnished with a groove-like perforation; columella with a 

 strong fold; shell umbilicated. Colour yellowish, cuticula darker. L. up to 12 mm. 



A. utriculus (Brocchi 1814) - Bulla Cranchii Leach 1847. 



(iylicluia Loven 1846. 



I. The central teeth of the radula with the margin scarcely incised in the middle; 

 the length of the shell > the double breadth; suture with a broad slit between 

 the outer lip and the body-whorl. 



A. Radula 3.1.1.1.3; shell with parallel sides, cylindrical, its length nearly 3 

 times the breadth; columella equallj^ bowed, without sinus near the lower 

 end but with a broad fold; spiral strite microscopical. Cuticula dark-yellow. 

 L. to 9 mm. C cylindracea (Pennant 1777). 



B. Radula 5.1.1.1.5; ends of the shell rounded; columella with a distinct si- 

 nus below; outer lip prominent över the apex; spiral strise fine but distinct; 

 shell broadest in the middle, its length = twice the breadth; columella with 

 a distinct fold; cuticula light yellow. L. 11 mm. C. alba (Brown 1827). 

 Shell cylindrical; columella with indistinct fold; apex broadly truncated; 

 cuticula thick, brownish. L. 8 mm. var. corticata (Möller 1842). 



II. The central teeth of the radula with the margin deeply incised in the middle; 

 the length of the shell < twice the breadth. Radula 2.1.1.1.2.^ 



A. Shell broadest below the middle; superior end a little narrower than the base; 



the strise equally close över the whole shell, not very deep; columella usu- 



ally bent to the right, by which the columellar sinus grows more concave. 



1. Outer lip much extended beyond the apex, angled above; superior end of 



the shell growing narrower from the middle to the apex; columellar rnar- 



^ For the synonyms of tlie following spccies see Leche 1878. 



