nearest relations of the Pteropoda. Some years afterwards, hc applicd ihis opinion to his classification 

 of the Molkisca ^). This view of the matter, combated by de Férussac -) and d'Orbigny '') vvith 

 many woi-ds and apodictic sentences, but not with arguments, found however defenders. 



First it was Deshayes *), who for the rest did not give observations of his own nor 

 procured new proofs — but it was Souleyet especially, who with extraordinary abilit)' defended 

 his opinion '") and, after a long series of researches of his own, adhercd to de Blainville's opinion. 



Clarke in England (1S51) had classified the Pteropoda among the Opisthobranchia, 

 but had not made researches himself, as far as I know at least, while Leuckart (1848) also 

 mentions the Pteropoda, as being an order among the Gastropoda. 



But in the many years that foliowed this period, there was scarcely a zoologist who 

 pronounced an opinion about de Blainville's views. The "class" of the Pteropoda remained 

 and it was not until a thirty years after, in 1880, that Spengel ") reckoned the Pteropoda 

 among the Gastropoda Euthyneura and, a short time after, Grobben '^) expressed his opinion 

 that the Pteropoda were an order of the Gastropoda, while he considers Gasteropteron as very 

 nearly related to the Pteropoda at any rata. 



Soon after, within a short time, two works appeared, which after that of Souleyet, 

 being founded on extensive researches of their authors, have attributed most of all to the opinion 

 that the Pteropoda belong to the Gastropoda. 



Boas's study **), which appeared in 1886, chiefly treated of the systematic position. But 

 his numerous arguments and the causal connection, pointed out by him, between the gradually 

 changing organisation and the pelagic way of living of the Pteropoda, made the correctness of 

 de Blainville's opinion indisputable. 



Just as DE Blainville had done already, Boas too regarded the Bulloidea as the 

 nearest relations of the Thecosomata '''). But he did not express an opinion on the question, 

 from which group of the Tectibranchia the Gymnosomata descended '"). Here the foUowing 

 question presents itself for the first time : whether the Thecosomata and Gymnosomata really 

 possess that near affinity which can justify their union to one group, the "Pteropoda". 



Boas was the first who indicated the great difference between these two sub-groups. 

 And in saying that the fins were not homologous, he proposed that henceforth ^^) the Thecosomata 

 should be called Eupteropoda and the Gymnosomata Pterota. 



i) Manuel de Malacologie et de Conchyliologie. 1825. The Pteropoda are regarded as an order, the Aporobranchia, and divided 

 into Thecosomata and Gymnosomata. The genus Liinaciiia^ called by him SpiyatcUa^ was classified by him as belonging to the Heteropoda. 



2) Hist. nat. générale et particuliere des Mollusques. p. 37. 



3) Voyage dans l'Amérique meridionale. Vol. V, p. 65. 



4) Encyclopédie Méthodique. Hist. Nat. des Vers. Paris 1830, Vol. II, p. 552. 



5) Voyage de la Bonite. Paris 1852, Vol. II, p. 88 — 8g. 



6) Geruchsorgane und Nervensystem der MoUusken. Zeitschr. Wissenschaftliche Zoölogie. Bd. XL, p. 373. Also see p. 366 

 and p. 381, note I. 



7) Morphologische Studiën über den Haru- und Geschlechtsapparat, sowie die Leibeshöhle der Cephalopoden. Arb. Zool. Inst. 

 Wien 1884, Bd. V, p. 61—67. 



8^ Boas. Spolia .\tlantica. Bidrag til Pteropodernes Morfologi og Systematik samt til Kundskaben om deres geografiske 

 Udredelse. Vidensk. Selsk. Skr. 6. Raekke. Bd. IV, i. 

 g) Op. cit. p. 36. 



10) Op. cit. p. 149. 



11) Op. cit. p. 13 and 14. 



