GASTEROrOPA. 039 



Family X. — Elysiad^. 



Animal shell-less, limaciform, with lio distinct mantle or 

 breathing-organ ; respiration performed by the ciliated surface 

 of the body ; mouth armed with a single series of lingual teeth ; 

 stomach central, vent median, sub - central ; hepatic organs 

 branched, extending the length of the body and opening into 

 the sides of the stomach ; sexes united ; male and ovarian 

 orifices below the right eye ; female orifice in the middle of the 

 right side ; heart with an auricle behind, and traces of an arterial 

 and venous system, eyes sessile on the sides of the head, 

 tentacles simple or obsolete.* 



Elysia, Eisso. 



Type, E. viridis, PI. XIII., Fig. 19. 



Synonym, Actseon, Oken. 



Animal elliptical, depressed, with wing-like lateral expan- 

 sions ; tentacles simple, with sessile eyes behind them ; foot 

 narrow. 



Distrihufion, 8 species. Britain, Mediterranean. On Zostera 

 and sea-weed, in the laminarian zone. Flaco-hranckus (ocellatus, 

 Eang.) Hasselt, Java; described as 2 inches long, with four 

 small tentacles ; the lateral expansions much developed and 

 meeting behind, the upper surface longitudinally plaited, and 

 forming, when the side-lobes are rolled together, a sort of 

 branchial chamber. 



AcTEONiA, Quatrefages. 



Example, A. corrugata, PI. XIII., Fig. 20. British Channel. 



Animal minute, leech-like ; head obtuse, with lateral crests 

 proceeding from two short conical tentacles, behind which are 

 the eyes. 2 species. 



Cenia, Alder and Hancock. 



Type, C. Cocksii, PL XIIL, Fig. 21. 

 Etymology, cenia, Falmouth. 

 Synonym ? Fucola (rubra) (Quoy). 



* Order Dermi-branchiata, Quatref. {PeUi-branchiata, A. and H.) M. Quatre- 

 fages erroneously described the Elysiadce as wanting both heart and blood-vessels, like 

 the Ascidian zoophytes ; with them he associated the family ^olida^ whicii he described 

 as having a heart and arteries, but no veins, their office being performed by lacunae of 

 the areolar tissue. In both families the product of digestion (chyle) was supposed to 

 be aerated in the gastric ramifications, by the direct influence of the surrounding 

 water. To this group, which has been since abandoned, he applied the name PhXeben- 

 terata {pMebs, a vein, entera, the intestines). 



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