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GASTEROPODA. 339 
FAMILY X.—ELYSIADA. 
Animal shell-less, limaciform, with no 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.* 
ELystA, Risso. 
Type, HE. viridis, Pl. XIII., Fig. 19. 
- Synonym, Acteeon, Oken. 
Animal elliptical, depressed, with wing-lke lateral expan- 
sions; tentacles simple, with sessile eyes behind them; foot 
narrow. 
Distribution, 8 species. Britain, Mediterranean. On Zostera 
and sea-weed, in the laminarian zone. Placo-branchus (ocellatus, 
Rang.) 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. 
CrentrIA, Alder and Hancock. 
Type, C. Cocksii, Pl. XIII., Fig. 21. 
Etymology, cenia, Falmouth. 
Synonym? Fucola (rubra) (Quoy). 
* Order Dermi-branchiata, Quatref. (Peilli-branchiata, A. and H.) M. Quatre- 
_ fages erroneously described the Elysiade as wanting both heart and blood-vessels, like 
i ee 
the Ascidian zoophytes ; with them he associated the family olide, which he described 
as having a heart and arteries, but no veins, their office being performed by lacunz of 
the areolar tissue. In both families the product of digestion (chyle) was supposed to 
be aérated in the gastric ramifications, by the direct influence of the surrounding 
water. Tothis group, which has been since abandoned, he applied the name Phleben- 
terata (phiebs, a vein, entera, the intestines). 
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