MOLLUSCA. 773 



Compare on this order CUVIEB Ann. du Mus. IV. 1804, pp. 223 234, 

 Mollusq., Mem. No. 3 ; PERON Ann. du Mus. xv. pp. 5769 (this writer 

 refers to this order several genera of Mollusca, which CUVIEB placed else- 

 where, and also the genus Callianira belonging to the Acalephce (p. 121); 

 J. F. J. KOSSE (prceside J. F. MECKEL) de Pteropodum ordine, &c. Halae, 

 1813, 4to; RANG Ann. des Sc. nat. v. 1825, pp. 283287; xn. 1827, pp. 

 320329, xni. 1828, pp. 302 319; P. J. VAN BENEDEN Exercises zoo- 

 tomiques (Nouv. Mem. de I'Acad. royale des Sc. de Bruxelles, xn. 1839) av 

 4 pi.; 'SouLEYET Comptes rendus, Tom. xvn. 1843, p. 662 et suiv. ; 

 HUXLEY Anatomy of Pteropoda in his paper on the Morphol. of the Cepha- 

 lous Moll., Phil. Trans., 1853, Pt. I. p. 39 and foil. ; GEGENBAUEB Unter- 

 such. Ueber Pteropoden u. Heteropoden, ein Beitr. Zur. Anat. u. EntwicJce- 

 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 GlOENI, ABILDGAARD, Caulina POLI). 

 Shell thin, pellucid, flat above, convex beneath, cloven on both 

 sides. Two large pinnae at the sides of mouth. Mantle produced 

 on both sides between the fissures of shell, with contractile appen- 

 dages. Branchiae 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 Hyalece, two 

 large laminae on each side, which meeting in the middle, cover the 

 dorsal and ventral surfaces of the shell. Whilst the animal 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 

 GECENBAUER. Besides these lamellae there are contractile processes 

 in Hyalece 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 pinnae at their base represents the foot 

 in this family. See GEGENBAUER 1. 1. s. 4, 5.] 



Sp. Hyalea tridentata LAM., Anomia tridentata FORSK. Icon. rer. nat. Tab. 

 40, fig. B, BLAINV. Malacol. PI. 46, fig. 2, DELLE CHIAJE Memorie, Tab. 

 80, fig. i, CANTRAINE Malacol. me"diterraneenne, Mim. de I' Ac. de Urux. 

 xni. PI. I. fig. 3 ; in the Med. Sea, &c. Comp. on the genus Hyalea, 

 BLAINVILLE in Diet, des Sc. nat. Tom. xxn. 1821, pp. 65 83. 



Cleodora. [Shell very fragile. Animal without appendages of 

 mantle produced over the shell. 



