ONCHIDIADiE. 



their geographical distribution. A few genera and species 

 are of maritime habits, requiring the presence of sea-water 

 for their existence, though, if kept immersed, they would 

 perish. 



onchidiam:. 



Most of the animals composing this family are true 

 sea-slugs, breathing by means of a pulmonary cavity, but 

 living immediately in contact with marine conditions. Cer- 

 tain forms of them live, however, inland, under old wood, 

 and in gardens. They are almost all tropical creatures, 

 and little known to the naturalists of Europe. They 

 are unprovided with shells, and have their dorsal surface 

 entirely covered with a fleshy disk or mantle. In aspect 

 they closely resemble some of the Elysiada, and consti- 

 tute a very natural link between the Gasteropoda opis- 

 thobranchiata and the Gasteropoda pulmonifera. 



ONCHIDIUM, Buchanan. 



Animal oblong ; unprovided with a shell, completely 

 covered above by a convex, coriaceous, usually tuber- 

 culated, rarely smooth mantle. Head provided with two * 

 retractile tentacles, bearing the eyes at their extremities ; 

 mouth covered by a buccal veil ; no horny jaws, a den- 

 ticulated tongue. Sexes combined ; orifices of repro- 

 ductive organs widely separated. Pulmonary orifice pos- 

 terior, and respiratory cavity placed behind the heart. 

 Vent posterior. 



This genus was founded by Buchanan for an animal 



