22 MOLLUSCA. 



long, through the lateral fissures of its shell ; they are productions of 

 the mantle. 



The species most known Anomia tridentata, Forskahl. ; Cavo- 

 lina natans, Abilgaard ; H. cornea. Lam. ; Cuv., Ann. du 

 Mus., IV. pi. 59; and Peron, lb., XV, pi. 3, f. 13. has a small, 

 yellowish, semi-diaphanous shell, found in the Mediterranean 

 and the Atlantic Ocean*. 



Cleodora, Peron. 



The Cleodorse, for which Brown originally created the genus Clio, 

 appear to resemble the Hyalese in the simplicity of their Avings, and in 

 the absence of tentacula between them ; it is also probable that their 

 branchiae are concealed in the mantle ; their conical or pyramidal 

 shell, however, is not cleft on the sides. M. Ray distinguishes 



Cleodora, properly so called, with a pyramidal shell, 



Creseis, with a conical and elongated shellf, 



CuviERA, with a cylindrical shell. 



Psyche, with a globular shell, and 



EuRYBiA, with a hemispherical shell. (I) 



It is thought that we may approximate to the Hyalege 



Pyrgo, 

 A very small fossil shell discovered by M. Defrance ; very thin, glo- 

 bular, and divided by a very narrow tranverso cleft, except before, 

 where it becomes a little widened(a^. 



* Add : Hyal. lanceolata, Lesiieur, Bullet., des Sc. June 1S13, pi. v, f, 3; — Hyal. 

 inflexa, lb., f. 4. 



N. B. The Glaucus, Carinaire, and Firole, refeiTed by Peron to the family of the 

 Pteropoda, belong to the Gasteropoda ; the Philliroe of the same author also 

 probably belongs to it. — His Calliumre is a Zoophyte. 



t It is probably near the Creseis, and perhaps even in the same subgenus, accord- 

 ing to Messrs Rang and Audouin, that Ave must place the genus Triptera of 

 Messrs Quoy and Ga\Tnard, which is referred by M. de Blainville to the family of the 

 Akerse. 



X See the Meip,, of M. Rang, Ann. des Sc. Nat., Novemb., 1827, and March 1828. 



N. B. Several Pteropoda have been discovered in a fossil state. M. Rang has 

 found, near Bourdeaux, Hyalete, Cuiiet-ue, and Cleodor<v. See Ann. des Sc. Nat. 

 August 1826. The Vaginella of Daudin is a Cresis according to M. Rang; it has, 

 in fact, all the characters of the latter. 



i^^ («) The Pteropodes constitute the first order of Lamarck's twelfth class, and 

 his division of this order into genera, is pi-ecisely the same as that given in the pre- 

 sent work, with the exception of the fossil genus added by Cuvier under the name of 

 Pyrgo. The general description of the order by Lamarck is as follows : — 



These Mollusca have no feet to crawl with, or arms to assist their motion or seize 

 their prey ; they have two opposite and simularly constructed fins adapted to swim- 

 ming; their bodies are free and floating. The Pteropodes are swimming Mollusca, 

 without the means of affixing themselves to other bodies, floating on the surface of 

 the sea and changing their position by ineans of their two fins or oars, which resem- 

 ble two wings placed on each side of the mouth in some and in others on each side 

 of the neck. He adds that in the Ayalda the head is so much concealed at the base 

 or point at which the fins are united that it appears obsolete, exhibiting consequently 

 an alliance between these animals and the Conchifer.T (the eleventh class of Mollus- 

 cous animals in his system). In the Cymbulia a little lobe which stands forward on 

 the posterior part, between the two tnie ^^^ngs, has been erroneously regarded as a 

 third fin. — Eng. Ed. 



