65 



cause tliat these "species" are now very vaguely knovvn, and will rcniain so in ilie üterature on 

 the Gymnosomata, without mucli possibihty that other naturahsts may recognize them with certainty. 



Though the studies ot' Cuvikr, Eschricut, dk Blainville, van Beneden, Souleyet, 

 Gegenhauk, Tkoschel, MCia.KR, 1m)i., Kroiin and Wagner — treating of whole groups or of 

 a single sjjecies only — have decidedly their merits, it was not until Boas and Pelseneer took 

 up their tasks, that the systematic classification of the Gymnosomata became clearly established. 

 Many of tlie species formerly described, ovight to be oblitcrated as real species, as their 

 characterization is insufficiënt, only a few should remain. On the other hand, the number ot 

 distinct species was importantly increased by the two last-mentioned zoologists. The result of their 

 monographs was, that twenty-one species were then really known. These species belonged to 

 five families and seven genera (Pelseneer). 



It may be supposed, however, that we know onl)' a small number of the species, really 

 existing in our seas. So, from the INlediterranean some peculiar larvae were formerly described 

 by Gegenbaur^), which since that time no naturalist has found again, at least not in the adult state, 

 but which belong to a genus Thiiptodoii, established by Boas "). Many of the species, badly 

 described by previous authors, may nevertheless represent curious types, about the characters 

 of which we unfortunately do not possess sufficiënt Information. According to the preliminary 

 notes of jNIeisenheimer, there has already been found in the material of the Valdivia Expedition 

 a new family, Pteroceanidae ^), and one new genus Schizobracliiuin ^). 



And finally the results of the Siboga Expedition show that explorations in a rather 

 limited area, as the eastern part of the Indian Archipelago, may procure very sufficiënt results. 

 For six genera, one of w^hich is new, are represented in the collection, while the number of 

 species amounts to eight. Plve of them had not been described before. 



1840. 

 1846. 

 1853- 



1855. 

 1856. 

 1858. 

 1862. 

 1863. 

 1871. 



1887. 



Family I. Pneumonodermatidae. 



Pneuinodennidac (part.) Gray, Synopsis of the contents of the British Museum, p. 86. 



Fneuniodeiniudae Agassiz, Nomenclator zoologicus, Inde.x, p. 299. 



Pneuinodcnnidae (part.) d'Orbigny in Ramon de la Sagra, Histoire physique, politique 



et naturelle de l'ile de Cuba, MoUusques, vol. II, p. 70. 

 Clioidea (part.) Gegenbaur, Untersuchungen über Pteropoden und Heteropoden, p. 212. 

 Cliidae (pai't.) Woodward, A Manual of the Mollusca, p. 208. 



PneiiiHoderinonidae (part.) H. and A. Adams, The Genera of recent Mollusca, vol. I, p. 62. 

 Pneiimodcnnidae Bronn, Die Klassen und Ordnungen des Thierreichs, Bd. III, p. 645. 

 Pnciiinodenimcfa Troschel, Das Gebiss der Schnecken, Bd. I, p. 56. 

 Pnenmoderniatidac Dall, Description of sixty new forms of Molluscs from the West 



coast of North America, Americ. Journ. Conch., vol. VI, p. 139. 

 Puciimojiodcnnatidae Pelseneer, Challenger Report, LVIII, p. 11. 



i) Untersuchungen über Pteropoden und Heteropoden, p. 95 — 97, pi. V, fig 



2) Spolia atlantica, p. 174. 



3) Zool. Anz., Bd. XXVI, p. 92—99. 



4) Ibid., p. 410 — 412. 

 SIBOGA-EXPEDITIE LU. 



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