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



Foot. — Anterior lobes large, broad in front, narrow and pointed behind, attached in 

 nearly their whole length ; posterior lobe short and pointed. 



Gills. — Quite absent. 



Proboscis short. 



Buccal Appendages. — Two or three pairs of retractile, glandular and sensory cones, 

 symmetrically inserted on the two sides of the buccal cavity. 



Jaio. — Absent. 



Radula always possessing in the adult a rather broad median tooth, without long 

 projecting spines, and rather resembling that of Halopsyche than of any other Gynmoso- 

 matous Pteropod. 



Hook-sacs of moderate size, with hooks of various lengths, so that when the sac is 

 evaginated the extremities of all the hooks reach to about the same level. 



The species of this family are generally described by zoologists under the name 

 of Clio. But this name was established by Browne in 1756, 1 and preserved by Linne 

 for a Thecosomatous Pteropod which most naturalists now name Cleodora pyramidata. 



As the description of the genus Cleodora by Peron and Lesueur was only published 

 in 1810, 2 the name Clio, on account of its priority, must be preserved instead of Cleodora, 

 which is more generally used. 0. F. Muller was therefore wrong when in 1776 3 he 

 applied the generic name Clio to a naked Pteropod, for this name was originally used for 

 a Thecosomatous form, and those zoologists who have followed him to this day are equally 

 in error. 



The Gymnosomatous Pteropods that are generally described under the name of Clio 

 must be placed in the genus Clione which Pallas established as far back as 1774 4 for the 

 type species, Clione limacina (his Clione borealis). 



For the various Gymnosomata which certainly belong to the genus Clione, it was 

 proposed to form new generic sections. Thus for some species whose buccal appendages 

 were not described, Quoy and Gaimard in 1825 established 5 the genus Cliodita, based 

 upon inexact differential characters. But these naturalists recognised later that 

 this group could not stand and they abandoned their genus altogether. 6 It is therefore 

 rather surprising to find that some more recent writers nevertheless preserve this 

 genus. 7 



On the other hand, several zoologists, without giving new generic names, have shown 



1 The Civil and Natural History of Jamaica, p. 386. 



2 Histoire de la famille des Mollusques Pteropodes, Ann. Mus. Hist. Nat. Paris, t. xv. p. 66. 



3 Faunae Danicse prodromus, p. 226. 



4 Spicilegia zoologica, fasc. x. p. 28. 



6 Description de cinq genres de Mollusques, Ann. d. Sci. Nat., st'r. 1, t. vi. p. 74. 



6 Voyage de decouvertes de l'Astrolabe, Zoologie, t. ii. p. 371, 1832. 



7 Gray, Catalogue of the Mollusca in the Collection of the British Museum, pt. ii., Pteropoda, p. 37; H. and A. 

 Adams, The Genera of Recent Mollusca, vol. i. p. 62 ; Bronn, Die Klassen und Ordnungen des Thierreichs, Bd. iii, 

 p. 645 ; Fischer, Manuel de Conchyliologie, p. 424. 



