Amono- them I can mention Simroth '), Crosse -), Grobben ^), Korsci-ielt *), and von 

 Ihering '). In most manuals anti icxt-botjks on zoology, the Pteropoda are mentioned either as 

 an order of the Gastropoda, or as a snb-order of ^the Opisthobranchia "). Yet the pretended 

 relationship of the Pteropoda with the Cephalopoda has given occasion to Schalfejeff '') to 

 draw the attention to the homology of the head-appendages of Clione with the arms of the 

 Decapoda. Smitii "), though referring to Pelseneer, calls the Pteropoda a separate class (a 

 mistake also made by Vogt and Yung some years before ^) ; while the title of Vitj.ot's work ^") 

 with respect to the classification of the MoUusca, does not seem justified in any respect, and 

 his systematization is anything but "actuel". 



That the Pteropoda descend from the Tectibranchia is no more a knotty point, but a 

 question on which most investigators have agreed. 



(Jn the polyphyletic origin of the Thecosomata and Gymnosomata and for that reason 

 their not admitting of the name "Pteropoda", only few have expressed an opinion. 



Though the foundation of Boas's opinion was said to be wrong, according to Pelseneer, 

 yet the latter has adduced sufficiënt proofs, which justify his opinion on the different origin of 

 both groups of Pteropoda. Later on, Simroth has acknowledged that the conformity between 

 Thecosomata and Gymnosomata was only apparent and is founded on convergency. 



Mazzarelli ^^), who examined the Aplj-sioidea, says that they are connected bv the 

 Xotarchidae with the Pteropoda ''), which is also mentioned by Pelseneer, who spoke about a 

 Notarchus-form as being the precursor of the Gymnosomata, Korschelt ^^), however, thinks that 

 embr}-ology speaks in favour of a very near affinit)- between the two groups and that the 

 Gj-mnosomata are phylogenetically younger than the Thecosomata and descend from these, an 

 assertion, formerly pronounced by Wagner ^*). xAs to myself, I have been able to study rather 

 extensively the anatomy of the Thecosomata as well as of the Gymnosomata. And because 

 nearly always — and with respect to the main points continually — I found Pelseneer's 

 researches affirmed by mine, I cannot but agree with him. And, referring to the results 

 mentioned above, I can only conhrm his assertions. For that reason I think it better, not to 

 use the name Pteropoda any longer, as it combines two groups, which in fact have no more 

 connection with each other, as is expressed by the characters of Bulloidea and Aplysioidea. 



i) Ueber einige Tagesfiagen der Malacozoologie, hauptsachlich Convergenz-Erscheiaungen betreffend. Zeitschr. Nalurw. Halle 

 18S9, Bd. 62, p. 65—97. 



2) A new classification of the Mollusca by W. H. Dall. Journ. Conchyl. 1S84. Paris 1889, Tomé 29, p. 82, 83. 



3) Zur Morphologie des Pteropodenkörpers. Arb. Zool. Inst. Wien 1S89, 8'-''' Bd., p. 155 — 157. 



4) Lehrbuch d. Vergl. Entw. Gesch. der Wirbell. Thiere. Spec. Theil. Jena 1893. (MoUuscs by' Korschelt). 



5) Sur les relations naturelles des Cochlides et des Ichnopodes. Buil. Sc. France. Tomé 23, p. 148 — 257. 



6) R. Hertwig (1894), The C.ambridge Natural History (Molluscs by Cooke) 1895, Parker and Haswell (Textbook of 

 Zoology, 1897), Goette (1902). Also in the Zool. Record since 1892, and in Lang's Lehrbuch der Vergl. Anatomie der Wirbellosen Thiere. 



7) Zur Anatomie der Clione Limacina Phipps. Zool. .Anz. 12 Jahrgang. p. 188 — 190. 



8) Report on the Marine MoUuscan Fauna of the Islands of St. Helena. P. Z. S. 1890. Pteropoda. p. 254. 



9) Lehrb. d. Pract. Vergl. Anatomie. Bd. I. Pteropoda. p. 828 — 852. 



10) La classification zoölogique dans l'état actuel de la science. Revue Biol. Lille 1891, 3'^"": année, p. 245 — 261. 



11) Monografia delle .\plysiidae del golfo di Napoli. Méra. Soc. Ital. Sc. dei XL (3). Tonio 9, N« 4, 1893. 



12) To my opinion it would have been bettev to say: Gymnosomata. 



13) Op. cit. p. 1046. 



14) Die Wirbellosen des Weissen Meeres. Bd. I, p. 119, 1885. 



