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



the Atlantic Ocean (the latter from Newfoundland), it is very difficult thoroughly to 

 appreciate them, so summary are the descriptions and figures of Eang ; but they appear 

 to resemble one another very closely. 



Verrill says 1 that he found the " Halopsyche" globulosa, Rang, on the shores of 

 Newfoundland and Nova Scotia. I have several times asked him for a specimen for 

 examination, but have never obtained one. 



Souleyet 2 thinks that Argivora parva, Lesueur, 3 from La Martinicpie, also resembles 

 Halopsyche ; but the information available in regard to this species is very fragmentary, 

 and its affinities cannot at present be decided. It is described, indeed, as a naked Cym- 

 bulia; it may, therefore, be a Tiedemannia (Gleba), that is, a Thecosomatous Pteropod. 



In conclusion, I must notice the genus Thliptodon, Boas, that I mentioned when 

 speaking of the larvae of the Pneunionoderniatidae. This genus is known only from its 

 larva, and thus its systematic position remains uncertain among the various families of 

 Gymnosomata. 



These larvae have a larger head than any other known larva of Gymnosomatous 

 forms. Its radula has a formula of 4:1:4; the median tooth is very short and with- 

 out denticles ; on the contrary the lateral teeth are very long, narrow, and slightly 

 bent at their free extremity. The jaw, the hook-sacs, and the buccal appendages have 

 never been seen ; perhaps some of them are wanting. The largest larvae have a foot, 

 the posterior lobe of which is well developed. The third or posterior ciliated ring has 

 the form of a star with three radii ; it may, therefore, be asked if the posterior gill of 

 the adult is not perhaps like that of Notobranchsea. 



Two larvae observed by Krohn 4 (one of them at Funchal, Madeira), possess a radula 

 which resembles that of the above larvae, formerly described by Gegenbaur 6 (and which 

 Boas called Thliptodon gegenbauri). 



With respect to the genus Cymodocea (Cymodocea diaphana, d'Orbigny), 8 it is a 

 form that is quite indeterminable from d'Orbigny 's description ; it was, moreover, 

 founded upon a mutilated specimen. 



It is very doubtful whether the organism called Homoderma 7 was a Pteropod at all; 

 it has no fins, and its mouth is lateral not axial. 



1 Notice of Recent Additions to the Marine Invertebrata of the North-East Coast of America, Proc. U.S. Nat. Mus., 

 vol. iii. p. 393. 



2 Histoire naturelle des Mollusques Pteropodes, pp. 71, 72. 



3 De Blainville, Manuel de Malacologie, p. 655. 



4 Beitrage zur Entwickelungsgeschichte der Pteropoden und Heteropoden, pp. 11, 14, p]. i. figs. 6, 11. 

 6 Untersuchungen liber Pteropoden und Heteropoden, pi. v. figs. 14-17. 



6 Voyage dans l'Amerique meridionale, t. v. p. 133, pi. ix. figs. 16, 17. 



7 Van Beneden, Exereices zootomiques, p. 54, pi. iii. figs. 4, 5. 



