390 ELYSIID^. 



stomach central, vent median, subcentral; 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. 



Subfamily ELYSIINM. 



Body very flat ; front narrow ; tentacles short, mostly ear- 

 shaped, the edges rolled up; eyes distant; genital orifice double, 

 behind, the right tentacle ; sides of the back winged, and a peri- 

 cardio-renal protuberance as in Placobranchus ; surface of the 

 back smooth, except an elevated line branching to the wings ; 

 pharynx and radula nearly as in Placobranchus, but usually no 

 crop : penis without sting. The genera are arranged as follows : 



Elysia, Risso. 



Syn. — Actseon, Oken, not Montfort. Aplysiopterus, Chiaje. 



Distr. — t sp. Europe, Philippines, Pelew Islands. E. viridis, 

 Mont, (xci, 40). 



Head rounded ; tentacles of moderate size ; vent anterior, 

 latero-dorsal, dorsal wings not much plaited, without bordering, 

 not continuous on the neck. 



TRiDACHiA, Desh. (Ptcrogasteron, Pease.) Wings much 

 plaited and undulated, continuous in front ; otherwise like 

 Elysia. E. crii^pata^ Orsted. West Indies. 



THURiDiLLA, Bergh. Head rounded, tentacles of moderate 

 size, vent posterior, median. E. splendida, Grube. Adriatic 

 Sea. 



ELYSiELLA, Bergh. Head carinated at the sides ; tentacles 

 minute, conical. E. pusilla, Bergh. Pelew Islands. 



ALLPORTiA, Tenison-Woods. Body expanded, thin, wholly flat- 

 tened anteriorly and posteriorlj'^ ; eyes submarginal. Tasmania. 



DiPLOPELYCiA, Morch, 18*72. 



Distr. — E. trigonura^ Morch. Mediterranean. 



Body compressed as in Scyllaea ; tentacles very strong, fan- 

 shaped, festooned at the edge ; no rhinophores, jaw or eyes ; 

 dorsal lobes with several fin-like processes ; under sides keeled ; 

 with similar processes on each side; tail triangular. 



Subfamily PLACOBRANCHIN^. 



Body flat, front large, with short eai'-shaped tentacles ; eyes in 

 the neck, approximate ; double genital orifice near the right ten- 

 tacle ; a distinct protuberance behind the neck, containing the 



