—_— 
390 ELYSUDA. 
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. 
SuspraMity HLYSIINA. 
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: 
EtysiA, Risso. 
Syn.—Acton, Oken, not Montfort. Aplysiopterus, Chiaje. 
Distr.—i sp. Europe, Philippines, Pelew Islands. . 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. (Pterogasteron, Pease.) Wings much 
plaited and undulated, continuous in front; otherwise like 
Elysia. £. crispata, Orsted. West Indies. 
THURIDILLA, Bergh. Head rounded, tentacles of moderate 
size, vent posterior, median. ZH. splendida, Grube. Adriatic 
Sea. 
ELYSIELLA, Bergh. Head carinated at the sides; tentacles 
minute, conical. #. pusilla, Bergh.’ Pelew Islands. 
ALLPORTIA, Tenison-Woods. Body expanded, thin, wholly flat- 
tened anteriorly and posteriorly ; eyes submarginal. Tasmania. 
DripLopetycra, Morch, 1872. 
Distr.—D. trigonura, Mirch. Mediterranean. 
Body compressed as in Scyllea; 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. 
SusraAMILty PLACOBRANCHAINE. 
Body flat, front large, with short ear-shaped tentacles; eyes in 
the neck, approximate; double genital orifice near the right ten- 
tacle; a distinct protuberance behind the neck, containing the 
