NOTES ON SOME BRITISH NUDIBRANCIIS, 365 



3. C. bicolor, Bergh (Japan). 



4. C. peachii, A. & H. (see Beaumont, I.e.). 



Uolis inornata, A. & H., and CuthoTut stinipsoni, Verrill (" Addns. to 

 Marine Fauna of N. America," in American J. of Sci. and Arts,yo\. xvii. 

 p. 314, 1879), possibly belong to this group, but are imperfectly de- 

 scribed, and the buccal parts unknown. 



The genus CufJionella was founded by Bergh for a single specimen 

 obtained by the ChaUenf/er in tlie Faroii Channel. Like Cuthona it has 

 a broad head, but it differs from both Cuthona and Cratcna in having 

 the foot truncated in front, jaws armed with several series (not a single 

 series) of denticles, and the anus opening on the back, not on the side. 

 It will be seen that all these characters, except the last, are very slight. 

 Friele (I.e.) examined specimens from the North Atlantic which had 

 the general characters of the Cratenidce and a dorsal anus, but a rounded 

 foot and a rather irregular denticulation of the jaw. Not wishing to 

 create a new genus for these trifling deviations, he referred the form to 

 Cuthonella, the characteristic of which thus becomes the position of 

 the anus, which is dorsal, but somewhat to the right of the median 

 line.* 



The genus thus contains — 



1. Cuthonella ahyssicola, Bergii. 



2. C. ferruginea., Friele. 



3. C. herghi, Friele. 



All from the North Atlantic, but not from British waters. 



There remains the large genus Cratcna, in which can be included 

 most of tlie forms not assigned to Cuthona, Cuthonella, and Amphorina, 

 though some of the less-known species of this group, such as EoJis 

 northuiiibrica, present remarkable peculiarities. In Cratena the head is 

 not broad, the cerata are not inflated, and the anal pnpilla is on the side, 

 not on the back. The radula is generally (but not always) short and 

 not markedly tapering. The teeth bear a few (rarely more than ten) 

 denticles on each side of a central cu.sp which is often not prominent. 

 As a rule the penis is unarmed, but in some cases, for which it hardly 

 seems worth while to create a new genus, it bears a style. The follow- 

 ing species seem referable to this genus with more or less certainty : — 



1. Cratena hirsuta, Bergh. Greenland. 



2. Cr. olrikki (Morcii). Greenland. 



3. Cr. pustidata (A. & II.). 



4. Cr. amcena (A. & II.). 



5. Cr.fructnosa, Bergh. Sargasso Sea. 



* I understand tliis to l)c tlie case in Cuthonella abyssicola, \'\\t Bergh'a statements in tlie 

 Challenger licpurt, on ]>. 'J.\ and ji. 25, are not quite consistent. 



