32 NILS HJ. ODHNER 



the sides beneath the tentacles", a character, which makes the 

 species easy recognizable at the first glance. This expansion of 

 the head is absent in the Norwegian form. 



Bergh was, however, in doubt whether his form was iden- 

 tical with that of CouTHOUY. He remarks: „The specimens which 

 I have examined, the same which were at Mørch's disposal, are 

 quite as impossible to identify with complete certainty w^ith 

 the present species as those which are referred below to Ae. 

 bostoniensis of Couthouy can with a certainty be identified as 

 the form of this author; for this purpose his statements are too 

 incomplete." 



After the issue of Bergh's work Gould & Binney published 

 in 1870^ two coloured figures of Couthouy's species [l. c, pi. 

 XVIII, figs. 264, 265). From them it appears that the anus is 

 situated behind the middle of the body and that the head is 

 expanded at the sides and the oral tentacles are fixed above 

 these expansions, that the foot is broad and suddenly tapering 

 -as in Bergh's species, while Sars' form has a slowly nar- 

 rowing posterior end of the body. Further, the papillae of the 

 former are more elongated than those of the latter, and agreeing 

 with Bergh's species. It is thus probable with a high degree 

 of certainty that the identity of Bergh's and Couthouy's species 

 is beyond doubt. On the other hand, it is proved that Sars' spe- 

 cies is distinct from both, and must receive a new name. 



The difference in the external habitus between the two 

 forms is shown in the figures 10 a and h. In C. borealis (10 6) 

 the oral tentacles are comparatively more separated, and stouter, 

 the foot is more slender than the respective parts in C. salmo- 

 nacea, and the head lacks the expanded cheeks. To these 

 external discrepancies may be added the distinct shape of the teeth 

 of the radula. In C. salmonacea the teeth are dark brown in 

 «colour, and the median tooth has a strong erect cusp with 4 — 6 



1 Rep. on tlie Invertebrata of Massachusetts. Boston. 



