36 



It may be remarked that not a single living animal was obtained by the expedition ; 

 nothing but empty shells have been found. This seems the more striking, since this species, 

 according to Boas ^) and several other authors, is very abundant in the warm seas. 



Hyalaea vmcroiiata, very obscurely described by Ouoy and Gaimard (see the synonyms) 

 has been regarded as a distinct species by d'Orbigny -). It must be noted, hovvever, that the 

 type of Ouov and Gaimard, did not differ from that of Lesueur, while d"Orbigny, who found 

 a somewhat different form, regarded it as the type, described by the zoologists of the 

 Astrolabe. The "species" of d'Orbigny is somewhat larger, more flattened, and the lateral 

 points are less divergent and more directed backwards than in Hyalaea trispinosa Lesueur. 

 Boas ') described two varieties : iiiiiuv, corresponding to the form of Lesueur, and major, 

 agreeing with Hyalaea niucronata d'Orbigny. As to the differences between these forms, I 

 must refer to Boas's important paper. But I have feit the truth there is in his words, that it 

 is in some cases impossible to decide, whether a specimen must be referred to major or to 

 minor. Neither the extension of the brown colour, nor the distinctness of dorsal grooves are 

 differences which hold good. Besides, the two varieties are not at all local; they occur together 

 in the Atlantic and in the Indian Ocean *). 



I have referred to major the specimens of stat.; 59, 88, 95, 100, 102; to miiior those 

 of stat. : 88, 211, 221, 300. 



In nearly all the specimens of major the long terminal point was broken off. According" 

 to Boas, this point is proportionally shorter than in minor. 



To show the different forms, I have figured some shells, seen from the dorsal side 

 (PI. II, figs. 27—31). 



2. Cavolinia (Diacria) quadridcnfafa^) (Lesueur). 



1821. Hyalaea quadridentata Lesueur in: DE Blainville, Dict. d. Sci. Nat. vol. XXII, p. 81. 

 1850. Cavolina quadridentata Gray, Catalogue of the Mollusca in the Collection of the British 



Museum, prt. II, Pteropoda, p. 8. 

 1852. Hyalaea inertnis Gould, The Mollusca and Shells of the U. S. Exploring Expedition 



under the command of WiLKES, pi. LI, fig. 604. 

 1877. Hyalaea iiiimita Sowerby, in Reeve, Conchologica iconica, vol. XX, Pteropoda, fig. 9. 

 1877. Hyalaea inter media Sowerby, Ibid., fig. 10. 

 1S79. Hyalaea costata Pfeffer, Uebersicht der auf S. M. Schift" "Gazelle" und von Dr. Jagor 



gesammelten Pteropoden, Monatsber. d. k. preuss. Akad. Wissensch. Berlin, 1S79. p. 234. 

 iS88. Cavolinia quadridentata Pelseneer, Chall. Rep. LXV, p. 78. 



Living animals: 



Stat. I. 7° 27'. 5 S., 113° 8'.5 E. I spec. 



Stat. 36. 7° 38' S., 117° 31' E. 2 spec. 



Stat. 37. Sailus ketjil. Paternoster Islands. 7 spec. 



1) Spolia atlantica, p. 95. 



2) Voyage dans r.Amcvique meridionale, vol. V, p. 108, pi. Vil, flgs. 6 — 10. 



3) L.C. s. 



4) Op. s. c, p. 96. 



5) d'Orbigny (Voyage d. r.*\mér. méiid. vol. V, p. 107) when speaking about Hyalaea trispinosa.^ whicli he compares with his 

 Hyalaea quadridentata (p. 98), gives the name quadiispinosa erroneously to this last species. This must he simply a mistake, and I cannot 

 admit this name into the list of synonyms. 



