66 



The characters of this family, which iiichides 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. Dexiobranchaea Boas'). 



2. Spongiobranchaea d'Orbigny'). 



3. Pneumonodernia 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 Scliizobrachiniii Meisenheimer ') really belongs to this famih-, 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 deem it, however, better to await Meisenheimer's extensive monograph on the 

 Gymnosomata of the Valdivia E.xpedition, before it can be ascertained with certainty whether 

 SchizobracJimni must be referred to the Pneumonodermatidae or not. 



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

 by the Siboga. It is the genus : 



Pneumonoderma Cuvier. 



1S04. Fncimwdcniia Cuvier, IMemoire concernant ranimal de I'Hyale, etc., Ann. ?^Iu.s. dTIist. 



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

 18 10. Fneiwioderma Peron and Lesueur, Histoire de ki famille des Mohusques Pteropodes, 



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

 18 1 5. Pne2imodermis Oken, Lehrbuch der Zoologie, Bd. I, p. 326. 

 18 1 5. Aegle Oken, Ibid., p. 326. 



18 1 7. Pneuinodermon Cuvier, Le Regne animal, vol. II, p. 380. 

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



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

 1879. Cirrifer Pfeffer, Ubersicht der wahrend der Reise urn die Erde auf S. M. Schiti" 



"Gazelle" und von Hin. Dr. JAGOR gesammelten Pteropoden, Alonatsber. Ak. 



Wiss. Berlin, p. 249. 



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

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

 its 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 



1) Vovliiufige Mittheilung iibev einige gymnosomen Pteiopoden, Zool. .\nz., Jalirg. \'III, p. 68S. 



2) Voyage dans rAm^rique mciidionale, vol. V, p. 130. 



3) Memoive coucei-nant ranimal de THyale, etc., Ann. Mus. d'Hist. Nat. Paris, vol. IV, p. 232. It has not become clear to 

 me, why Pelseneer has used the name Pncumoiiodcriiia and not Pncumoilcimon. 



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



5) Spolia Atlantica. p. 151 — 155. 



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



