ONCIDIUM. 95 



foot much narrower than the mantle : respiratory orifice under 

 the hinder edge of the mantle : vent near the respiratory orifice. 

 Hermaphrodite, with mutual congression, the reproductive or- 

 gans being separate. 



Shell none. 



Genus ONCI'DIUM* {Onchidium) Buchanan. 



PL III. f. 5. 



Body oblong, convex, usually tuberculous : head covered by 

 the mantle when the animal contracts itself; it is furnished 

 with a veil, which is formed of two triangular and compressed 

 lobes: mouth destitute of jaws: gizzard muscular. 



Established by Dr. Buchanan in the transactions 

 of the Linnean Society/ and adopted by Cuvier and 

 Lamarck. The type on which it was founded is a spe- 

 cies discovered by Peron on rocks in the Isle of France. 

 Audouin believed that the tubercles on the hinder part 

 of the mantle in the typical species are true gills, which 

 exist independently of the pulmonary apparatus ; but 

 other species are quite smooth. It is not improbable, 

 however, that the skin or outer integument of the body 

 may serve the purpose of respiration while the animal 

 remains under water. 



It is the genus Peronia of De Blainville; at least, 

 no character has been given by him or the Messrs. 

 Adams by which that genus can be distinguished from 

 Oncidium. 



Oncidium Cel'ticum-j-, Cuvier. 



Onchidium Celticum, Cut. Kegne An. iii. p. 46, footnote (indicated but 

 not described) ; F. & H. iv. p. 3, pi. FFF. f. 6. 



Body thick, somewhat extensile, greyish-olive ; it is closely 



* Diminutive, from oy/cos, a tumour or swelling, 

 t Inhabiting the Celtic region. 



