28 NILS ODHNER, NORTHEBN AND ARCTIC INVERTEBRATES III. OPISTHOBRANCHIA ETC. 



Aeolis CuviER 1802. 

 Aeolidia Cuvier 1817. 



The rhinopliores < the oral tentacles, inserted close by each other. Papillae 

 in about 20 transverse rows, covering nearly the whole back. Colour varying, usu- 

 ally marbled with white, gray and violet; rhinophores and papillae dark with white 

 ends. L. to 80 mm. Ae. papillosa (Linné 1766). 



Åeolidiella Bergh 1874='. 



Papillse in about 14 rows, containing 10 — 12 papillse each; the rhinophores = 

 the oral tentacles. united at the base. Colour påle reddish, papillse greenish with 

 brown and white spöts. Teeth of the radula with about 30 denticles on each side. 

 L. up to 45 mm. Ae. glauca (Ålder & Hancock 1845''). 



Ciitlioiia Ålder & Hancock 1853. 



I. Head as broad as the foot, with the sides produced. 



A. Body depressed; papilla^ clavate, in 8 — 10 close rows. Colour yellow or brown; 

 papillse rosy, brown-spotted. Radula with 69 plates ; the teeth elongated, with 

 a short middle-spine and 5 — 8 denticles on each side. L. 10 mm. 



C. nana (Aldeb & Hancock 1842). 



Pl. Il lig. 2U. 



B. Body tapering backwards ; gills in numerous rows, each containing about 8 — 9. 

 Colour light yellow, at the posterior of the back rosy; papillse with yelJow- 

 ish brown liver-processes and white tips. Radula with 18 plates; the teeth 

 produced, with a long central spine and about 8 small denticles on each side. 

 L. 12 mm, C. Peachi (Ålder & Hancock 1848). 



II. Sides of the head not produced; body slender; gills linear in 10 — 11 close rows. 

 Colour yellowish white, papillse purple, their tips orange with a white ring, rhino- 

 phores rosy, oral tentacles white. Radula with 80 plates; the teeth arch-shaped 

 with 3 marginal denticles on each side. L. 15 mm. 



C. aurantiaca (Ålder & Hancock 1842). 



Cratena Bergh 1864. 



I. The rows containing at most 5 papillse. 

 A. Oral tentacles < the rhinophores. 



1. Papillse cylindrical in 6^ — 8 rows of 3 — 4 each; foot with the anterior 

 angles obtuse. Colour yellowish Avith opaque white döts, rhinophores 

 yellow, spotted with white and with a red ring in the middle; papillse 

 yellowish brown with light tips and with bands of olive-coloured granulate 

 döts; radula with 57 plates, teeth with 6 denticles on each side. L. 10 mm. 



C. olivacea (Ålder & Hancock 1842). 



2. Papillse subconical in 9 — 10 rows, 5 in each row; the anterior angles of 

 the foot a little produced. Colour yellowish white, the rhinophores with 

 white ends ; papillse violet, granulate in the middle, bluish outwardly, their 



