GASTEEOPODA. 839 



Family X. — Elysiad^e. 



Animal shell-less, limaciform, mth. no distinct mantle or 

 breatMng-organ ; respiration performed by the ciliated surface 

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

 stomach central, yent 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 tho 

 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. yiridis, PL XIII., Fig. 19. 



Sijnonym, Actseon, Oken. 



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

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

 narrow. 



Disfrihution, 8 species. Britain, Mediterranean. On Zostera 

 and sea-weed, in the laminarianzone. Flaco-lrancJius (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, PL 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 XIII., Fig. 21. 

 Etymology, cenia, Falmouth. 

 Synonym? Fucola (rubra) (Quoy). 



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

 fages erroneously described the Ehjsiadee as wanting botli heart and blood-vessels, like 

 the Ascidian zoophj-tes ; with tliem he associated the family ^olidte, which he described 

 as having a heart and arteries, but no veins, tJieir office being performed by lacunse of 

 the areolar tissue. In botli 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, wliich has been since abandoned, he applied the name P/dehcri' 

 ternta [phlehs, a vein, entera, the intestines). 



Q 2 



