67 



these forms I shall have lo discuss further on, as they were oblained within the area of 

 exploration of the SiboCTa. 



The material of ihis expedition contains three species, two of which are new. One 

 species, recorded from the Ivisl-lndian Arrhipelago has not been obtained. 



I mav lay stress on tiie fact that it is often very difficuU to distinguish the species 

 from eacli other. The body being strongly contracted, it is by no means easy to discover the 

 exact shape of the lateral and tlie posterior gill; and the buccal appendages can be examined 

 generaUy only by dissection of the head-cavity, in which they are retracted. Added to this 

 the excessive smahness of some species (not yet 2 mm.), one can understand the difficulty 

 with which the systematic classification of Pnetiinonodervia is connected. 



I . PncniiionoderDia pcroni (Lamarck). 



327- 



18 15. Aegle cucullata Oken, Lehrbuch der Zoölogie, Bd. I, p. 



1819. Pneiimodcruion pcroni Lamarck, Histoire naturelle des Animaux sans Vertèbres, vol. 



VI, p. 294. 

 1887. Pneuinodeniia pcroni Fischer, Manuel de Conchyliologie, p. 423. 

 1887. Pncnuionodcnna pcroni Pelseneer, Challenger Rep. LVIII, p. 29, pi. II, fig. 2. 



Living animal: 



Stat. 109. Pulu Tongkil, Sulu Archipelago. i spec. 



Only one specimen was caught during the whole cruise of the expedition. It is very 

 contracted ; the skin is phcated in large folds and of a greyish colour. In the shape of the 

 gills, and in the disposition of the acetabuhferous appendages, the specimen entirely agrees 

 with the descriptions of BoAS and Pelseneer. The length Is only 8 mm. 



*2. PnaLmonodcriiia incditcrranc2iiii (van Beneden). 



183S. Pncuinodcnnon mcditerrancum van Beneden, Note sur une nouvelle espèce de Pneumo- 



derme, Mém. Acad. Sci. Brux., vol. XI, p. 13, pi. III, figs. i — 2. 

 1852. Pncnniodcrmon pcronii (part.) Souleyet, Voyage de la Bonite, vol. II, p. 274, pi. XIV, 



figs. 13, 14, 16. 

 1852. ? Pncumodcrinon pcrojiii (part.) Rang, Histoire naturelle des Mollusques Ptéropodes, 



pi. XI, figs. 14 — 19. 

 1855. Pncjimodermon mediterrancuin Gegenbaur, Untersuch. über Pterop. u. Heterop. p. 213. 

 1859. SpongiobrancJiea austrahs (part.) Chenu, Manuel de Conchyliologie, vol. I, p. 116, fig. 509. 

 1873. Pneumodernion peronii Costa, Pteropodi della Fauna di Napoli, p. 22, pi. V, fig. i — 3. 

 1886. Pncumodcrinon inacrocotylum Boas, Spolia atlaiitica, Bidrag til Pteropodernes Morfologi, 



etc, K. dansk. Vidensk. Selsk. Skr., 6 Raekke, Bd. IV, p. 152. 



1886. Pneuiiiodeniion andebardi Locard, Prodrome de la Malacologie frangaise, Mollusques 



marins, p. 19. 



1887. Fncuiiiodcniia vieditcrraneum Fischer, Manuel de Conchyliologie, p. 423. 



1887. Pneumonodcrma mediterraneuin Pelseneer, Chall. Rep. LVIII, p. 26, pi. I, fig. 8. pi. II, fig. i. 



According to Boas, this species has been caught in the Indian Ocean (5°24'S., 87° 56' E. 

 and 10° S., 104° E.) and in the China Sea (16° N., 11 5° 20' E.). 



