66 



The characters of this family, which iiicludes a rather large number of species, were 

 established by Pelseneer. According to his researches and those of Boas, three genera may be 

 properly distinguished : 



1 . Dcxiobrancliaca Boas '). 



2. Spongiobrancliaca d'Orbigny '). 



3. Pneuinouodcriua Cuvier ''). 



These three genera are all characterised by the presence of suckers on the ventral side 

 of the buccal cavity and of a gill on the right side. 



If the genus ScJiizobraclnum Meisenheimer ') really belongs to this family, the possession 

 of a lateral gill is no longer characteristic of the Pneumonodermatidae, and so only the suckers 

 remain, either situated on buccal appendages or directly inserted on the ventral wall of the 

 buccal cavity. I deern it, hovvever, better to await Meisenheimer's extensive monograph on the 

 Gymnosomata of the Valdivia Expedition, before it can be ascertained with certainty whether 

 Schizobrachüiiii must be referred to the Pneumonodermatidae or not. 



Of the four genera above named, only one was represented in the material coUected 

 by the Siboga. It is the genus ; 



Pneumonoderma Cuvier. 



1804. Pncumoderma Cuvier, Mémoire concernant Tanimal de l'Hyale, etc, Ann. Mus. d'Hist. 



Nat. Paris, vol. IV, p. 232. 

 18 10. Pneumodertiia Péron and Lesueur, Histoire de la familie des Mollusques Ptéropodes, 



Ann. Mus. Hist. Nat. Paris, vol. XV, p. 65. 

 18 15. Pneiimodeniiis Oken, Lehrbuch der Zoölogie, Bd. I, p. 326. 

 18 15. Aegle Oken, Ibid., p. 326. 



18 17. Pneutiiodennoii Cuvier, Le Règne animal, vol. II, p. 380. 

 1846. Pneiiinonodcnna Agassiz, Nomenclator Zoologicus, Index, p. 299. 



1855. Pncifinouodennuvi Herrmannsen, Indicis generum Malacozoorum primordia, vol. I, p. 309. 

 1879. Cirrifer Pfefter, Übersicht der wahrend der Reise um die Erde auf S. M. Schift" 



"Gazelle" und von Hrn. Dr. J.\GOR gesammelten Pteropoden, Monatsber. Ak. 



Wiss. Berlin, p. 249. 



This genus is chiefly characterised by the presence of twro acetabuliferous buccal 

 appendages, the suckers of which do not increase in size from the base of the appendage to 

 lts distal extremity — and by the great development of the lateral and the posterior gill. 



After the investigations of Boas '') and Pelseneer ") we now know six species of this 

 genus. Most of the forms, described by authors previous to the above-mentioned zoologists, were 

 either identical with other species already known or too insufficiently characterised. Some of 



i) Vuilaufige Mittheilung über einige gymiiosomea Pteropoden, Zool. .\nz., Jahig. V'III, p. 688. 



2) Voyage dans rAmérique meridionale, vol. V, p. 130. 



3) Mémoire concernant l'animal de l'Hyale, etc, Ann. Mus. d'Hist. Nat. Paris, vol. IV, p. 232. It has not become clear to 

 me, why Pelsexeek has used the name P/witnio/ioiicrnia and not Pncttmodermon. 



4) Zool. Anz., Jahrg. XXVI, p. 410 — 412. 



5) Spolia Atlantica. p. 151 — 155. 



6) Challenger Report LVIII, p. 23 — 32. 



