—_ a 
MOLLUSGA. tia 
Compare on this order Cuvier Ann. du Mus. Iv. 1804, pp. 223—234, 
Mollusq., Mém. No. 3;—P£Ron Ann. du Mus. XV. pp. 57—69 (this writer 
refers to this order several genera of Mollusca, which Cuvinr placed else- 
where, and also the genus Callianira belonging to the Acalephe (p. 121); 
J. F. J. Kosse (preside J. F. Mxcxrt) de Pteropodum ordine, &c. Hale, 
1813, 4t0; Rana Ann. des Se. nat. V. 1825, pp. 283—287; xit, 1827, pp. 
320—329, XIII. 1828, pp. 302— 319 ;—P. J. VAN BENEDEN Exercises zoo- 
tomiques (Nouv. Mém. de Uv Acad. royale des Se. de Bruselles, x11, 18 39) av. 
4 pl.;—Sovunryer Comptes rendus, Tom. XvIt. 1843, p- 662 et suiv. ; 
Huxiey Anatomy of Pteropoda in his paper on the Morphol. of the Cepha- 
lous Moll., Phil. Trans., 1853, Pt. 1. p- 39 and foll.; GrecENBAUER Unter- 
such. Ueber Pteropoden u. Heteropoden, ein Beitr. Zur. Anat. u. Entwicke- 
lungsgesch. dieser Thiere, mit 8 lithogr. Taf. Leipzig, 1855, 
Family I. Hyaleacea. Pteropods with head indistinct, included 
posteriorly in a thin shell. 
Hyalea Lam. (Cavolina GIOENI, ABILDGAARD, Caulina Poti). 
Shell thin, pellucid, flat above, convex beneath, cloven on both 
sides. Two large pinne at the sides of mouth. Mantle produced 
on both sides between the fissures of shell, with contractile appen- 
dages. Branchiz arranged in a circle round the other viscera, 
fasciculate. 
[In this family, the mantle, besides forming the general covering 
for most of the viscera, is inflected anteriorly on the ventral surface 
to form a pocket, which is the branchial cavity. The mantle sends 
processes laterally through the fissures of the shell in Hyalew, two 
large lamine on each side, which meeting in the middle, cover the 
dorsal and ventral surfaces of the shell. Whilst the anima] is alive 
this is their constant position, but when it dies they are retracted 
within the shell, and hence were not known until observed by 
GEGENBAUER. Besides these lamellze there are contractile processes 
in Hyalee often six times the length of the body. They are fre- 
quently mutilated. All the different processes are less developed 
in Cleodora and Creseis, and none of them are thrown round the 
shell. A lobe that joins the pinnz at their base represents the foot 
in this family. See Gucrnpauer lls. 4, 5.] 
Sp. Hyalea tridentata Lam., Anomia tridentata Forsk. Icon. rer. nat. Tab, 
40, fig. B, Buatnv, Malacol. Pl. 46, fig. 2, Denix CHIAJE Memorie, Tab, 
80, fig. 1, CANTRAINE Malacol, méditerranéenne, Mém. de VAc. de Brux. 
xul, Pl. 1. fig. 3; in the Med. Sea, &e. Comp. on the genus Hyalea, 
BLAINVILLE in Dict. des Se. nat. Tom. Xx1I. 1821, pp. 65—83. 
Cleodora. [Shell very fragile. Animal without appendages of 
mantle produced over the shell. 
