21 



The shells of these larval forms are minute, left-handed, sometimes transparent; so 

 there is some resemblance with the shells of Limacinidae, hut the thickened margins of 

 "■ Agadina" form the difference. Besides, the operculum in "■ Agadina' is horny and not thin 

 and glassy as in the Limacinidae; it has a large nucleus, left-handed, and is attached 

 more strongly to the foot by means of a knob. Another difference from the Limacinidae 

 is the fact that the operculum, very distinctly concave at the outside, is circular and not 

 more or less semilunar. 



H. SiMROTH ') made already known several larvae with a left-handed shell, about which 

 it is very difficult to decide to what genus they must be referred. Perhaps they belong to 

 marine streptoneural Gastropods with a right-handed spire, but the initial portion of which is 

 coiled to the left, as it has been suspected by Pelseneer -). The operculum is left-handed, and 

 besides, the beginning of its spiral is turned to the columella, as occurs in ultra-dextral forms. 



Family IL Cavoliniidae. 



1841. Hyalidae (part.) d'Orbigny, in: Histoire physique, politique et naturelle de I'ile de Cuba, 



par Ramon de la Sagra, Moliusques, vol. I, p. 70. 



1842. Cavolinidae d'Orbigny, Paleontologie frangaise, Terrains cretaces. vol. 11, p. 4. 

 1842. Cleodoridac Gray, Synopsis of the contents of the British Museum, p. 92. 



1S54. Hyalaeacea Troschel, Beitrage z. Kenntn. der Pteropoden. Arch. f. Naturgesch., Jahrg. 



XX, p. 196. 

 1856. Hyaleidae (part.) Woodward, Manuel of the Mollusca (2'«l Edit. p. 348). 

 1869. Cliidae Jeffreys, British Conchology, vol. V, p. 118. 

 1 875. Ortlioconques Fol, Sur le developpement des Pteropodes, Arch. d. Zool. exp., ser. i, 



vol. IV, p. 177. 

 1885. Hyalaeidae Boas, Spoiia atlantica, Bidrag til Pteropodernes Morfologi og Systematik samt til 



Kundskaben om deres geografiske Udbredelse, Vidensk. Selsk. Skr., 6. Raekke, I V, i . p. 5 i . 

 1888. Cavoliniidae Pelseneer, Challenger Rep. LXV, p. 41. 

 incl. Cuvieridae Gray, 1842 ^^ Triptcridae Gray, 1850. 



This family formerly included many more genera, than really belong to it. D'Orbigny 

 (see the list above) classed all the Thecosomata, with which he was acquainted, among his 

 Hyalidae (also Cymbtilia and Limacind) and Souleyet ^) referred to his "famille des Hyales" 

 also Limacina and "■ Spirialis'\ while Woodward (see above) included in his family; Euribia 

 Rang (^ Halopsyche Broun), Cyinbulia and Tiedemannia Delle Chiaje (^^ Gleba Forskal). 



Bo.\s and Pelseneer, however, have defined more strictly the limits of the Cavoliniidae. 

 The forms, composing this family, are characterised by their external, calcareous, bilaterally- 

 symmetrical shell ■*), which is not coiled, but in some cases straight, in others provided with a 



1) Die Gastropoden der Plankton-Expedition 1895. 



2) Ch.iUengei- Rep. LXV, p. 40. 



3) Llistoire naturelle des Moliusques Pteropodes, p. 32. 



4) Some asymmetry in the shell is found in Clio (Styliola) sulmlii.^ in "■Clcodora''^ Scheeiei Munthe (Pteropoder i Upsala 

 Universitets zoologiska Museum, Bihang till K. Svenska Vet. Akad. Handlingar, Bd. 13, afd. IV, n" 2, p. 1 8 — 19, fig. 15), aud in 

 '^Pteurofiis hargcrV Verrill (Catalogue of Marine Mollusca added to the fauna of the New England region, during the past ten years, 

 Transactions Connectic. Acad. vol. V, prt. 2, 1882, p. 555). 



