441; PHILOSOPHY OF IfOOLOGY. 



opening of the anus and oviduct are at the base of the right 

 fin. 



The Hydlea tridentata, the best known species of the 

 genus, was first noticed by Forskal, in his Descriptiones 

 AnimaUum^ p. 124, as an anomia, and inhabiting the Me- 

 diterranean, The same species washkewise taken in abun- 

 dance in the Gulf of Guinea, by the expedition under Cap- 

 tain TUCKEY. 



(2.) Tunic destitute of a shell. 

 A. Fins double. 



Posterior extremity with leaf-like ridges. 

 8. Pneumodermon. — Head with two bundles of tenta- 

 cula. 



The body is oval, with a narrow neck, and a fin on each 

 side. The mouth is nearly terminal, furnished on each 

 side with a fleshy lip, and beneath, with a fleshy chin. 

 Each tentaculum consists of a filament, with a tubercle at the 

 end, pierced by a small hole, and considered as exercising 

 the office of a sucker. Cuvier, in his Memoir sur VHayle 

 et Le Pneumoderme, considered the leaf-like ridges which 

 occur on the caudal extremity of the body, as the branchia?, 

 and even describes the pulmonary vein which conveys the 

 blood from these to the heart. But, in his Regne Animal, 

 he states it as the opinion of his assistant, M. Blainville, 

 that the fin-like expansions of the neck contain the bran- 

 chiae on their surface, as in the case of Clio. The rectum 

 and oviduct terminate under the right wing. Cuvier has 

 figured and described the only known species, which he 

 terms Pneumodermon Peronii, the trivial name being in 

 honour of the discoverer, M. Peron. 

 Posterior extremity simple. 



9. Cmo. — Body ovate, with the tunic elongated and 

 membranaceous. 



