38 THE VOYAGE OF H.M.S. CHALLENGER. 



Description. — Body ovate, contracted and pointed at the posterior extremity. 

 Visceral mass not extending to this extremity. No dorsal spot as in the two foregoing 

 families. Head short and swollen ; neck short. 



Foot. — Posterior lobe long, pointed at its free extremity ; anterior lobes long, free for 

 a great part of their length ; between them, on the foot, a small tubercle. 



Fins large, broad and rounded at their free extremity. 



Posterior Gill. — Three longitudinal membranous crests which meet together at the 

 posterior extremity of the body, and spread over about the posterior third of the body ; 

 of these crests, one is median and dorsal, the two others lateral (right and left) and 

 symmetrical, the ventral side being naked. The dorsal crest alone is fringed, the fringes 

 of the right side alternating with those of the left side ; the two lateral crests are simple, 

 without fringes or foldings. There is no lateral gill. 



Buccal Appendages. — One pair of thick, short (perhaps shortened by shrinking in 

 the alcoholic specimens), symmetrical cones, inserted on the lateral sides of the wall of the 

 buccal cavity, flattened on their median side, and with a smooth surface. 



Radula, Jaw, and Hook-sacs unknown. I had only a single specimen for examina- 

 tion from the Challenger collection (type of NotobrancJisea inopinata), and one specimen 

 in the Brussels Museum (type of NotobrancJisea macdonaldi); thus I was not able to 

 extract the horny buccal organs of these specimens without damaging them. But from 

 the shortness of the neck it may be inferred that the hook-sacs are also rather short ; and 

 from the general resemblance of Notobranchasa to Clione, I think it probable that the 

 radula of the adult, in this faindy, always possesses a median tooth, and that the jaw is 

 perhaps absent. 



As these horny pieces are important, from a systematic point of view, for the com- 

 parison of genera and species, they ought to be examined in the first specimen which is 

 gathered in the future. 



Notobranchaea, 1 Pelseneer. 



1825. Clio, Rang (pars), Description d'un nouveau genre de la classe des Pt^ropodes et de deux 

 especes nouvelles du genre Clio, Ann. d. Sci. Nat., ser. 1, t. v. p. 286. 



1863. Clio, Macdonald (pars), On the Zoological Characters of the living Clio caudata, Trans. 

 Roy. Soc. Edin., vol. xxiii. p. 186. 



1886. Notobranchsa, Pelseneer, Description d'un nouveau genre de Pteropode Gynmosonie, 

 Bull. Sci. depart. Nord, p. 224. 



Characters and Description as for the family Notobranchseidas. 



I made this genus known in June 1886, founding it on a Gymnosomatous Pteropod 

 from the North Atlantic, which was sent to the Brussels Museum by the U.S. National 

 Museum. 



I have previously said that many specimens of Pteropods were prepared for micro- 



1 From vinos, back, and /3g«yx'«. gill. 



