REPORT ON THE PTEROPODA. 39 



scopical examination (stained and mounted in Canada balsam) by R. von Willemoes 

 Suhm, without any previous examination. It was in this collection of preparations, 

 which was sent to me along with the alcoholic specimens of Pteropods, that I found the 

 following specimens of Gymnosomata from four Stations : — 



Station 170, ..... Halopsyche gaudichaudi. 



Station 240, . . . . . Pneumonoderma pacificum. 



Between Stations 332 and 333, March 11, 1876, Spongiobranchaea australis. 



Near Station 354, May 7, 1876, . . Pneumonoderma violaceum. 



A little after the publication of my Description d'un nouveau genre de Pteropode 

 Gymnosome, and when the text of this Report was already far advanced, I re-examined 

 this series of preparations to make certain that no Gymnosomatous Pteropod had 

 escaped me. It was then that I found a specimen of a naked Pteropod from the 

 North Atlantic, which was in such a state, from the colouring and the compression 

 between the slide and cover-glass, that I did not recognise it on the first examination. 



When this specimen was freed from the balsam, by dissolving the latter in chloroform, 

 I was able to study it more easily, and found that it belonged to the new genus I had 

 just established. 



As the form that I described in June 1886 was only obtained in 1883, and the 

 Challenger specimen from the Pacific was caught on June 24, 1875, the priority 

 of the discovery of the genus N otobranchsea belongs to the Challenger Expedition, 

 and to it also would have belonged the nominal priority, if the single specimen from 

 Station 242 had not unfortunately been stained and compressed on the glass slide 

 instead of being preserved in alcohol. 



The two known species of the present genus are distinguished as follows : — 



I. Dorsal crest of the gill with large and long fringes ; anterior lobes of the foot 



free for two-thirds of their length, ..... Notobranchxa macdonahli. 



II. Dorsal crest of the gill with short and small fringes ; anterior lobes of the foot 



free for half their length, ...... Notobranchxa inoyinata. 



1. Notobranchsea macdonaldi, Pelseneer (PI. III. figs. 3, 4). 



1884. Clione longicaudatus, Verrill, Second Catalogue of the Mollusca recently added to the 



Fauna of the New England Coast, Trans. Connect. Acad. Arts 

 and Sci., vol. vi. p. 215. 



1886. Notobranchxa macdonaldi, Pelseneer, Description d'un nouveau genre de Pteropode 



Gymnosome, Bull. Sci. depart. Nord, p. 225. 



Head round, neck contracted. 



Foot with anterior and posterior lobes long and pointed at their free extremity ; 

 anterior lobes free for the two posterior thirds of their length ; between these two lobes 



