212 MOLLUSCA. 
is inferior, sessile, and larger than the thorax. The single 
ovarium is pedunculated. SS. astralius, Sav. tab. iii. f. 2., 
brought from New Holland, by M. Peron, is the only known 
species. 
6. Branchial orifice only furnished with six rays. 
(A.) Body pedunculated. System single, circular, and 
terminal. 
Genus Synoicum.—aAnal orifice rayed. 
The body is cylindrical. The anal orifice has six very 
unequal rays; the three largest forming the exterior mar- 
gin of the central star. The stomach is simple. The angles 
of the branchial meshes destitute of the papille. Ovarium 
single, sessile attached to the bottom of the abdomen, and 
descending perpendicularly. The S. turgens of Phipps is 
the type. 
Genus SypNeEuM.—Anal orifice simple and tubular. 
The body is inversely conical. The stomach surrounded 
with glands. Intestine spirally folded. Ovarium peduncu- 
lated. The S. turbinatum is the only known species, and 
was sent to Savigny by Leach from the British seas. 
(B.) Body sessile, polymorphous. 
(a.) Each system with a central cavity. 
GEnvus PoLtycLinum.—Systems numerous, convex stellu- 
lar. Individuals arranged irregularly round the common 
centre. Abdomen inferior pedunculated, and less than the 
thorax. Ovarium single, pedunculated, and attached to the 
side of the abdominal cavity, and drooping. 
M. Savigny describes one species from the Mauritius, and 
five from the Gulf of Suez. 
(4.) Systems destitute of the central cavity, and the an- 
gles of the branchial meshes without papille. 
