212 MOLLUSCA. 



is inferior, sessile, and larger than the thorax. The single 

 ovarium is pedunculated. S. aslralius, Sav. tab. iii. f. 2., 

 brought from New Holland, by M. Peron, is the only known 

 species. 



b. Branchial orifice only furnished with six rays. 



(A.) Body pedunculated. System single, circular, and 

 terminal. 



GENUS SYNOICUM. Anal 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 papillae. Ovarium 

 single, sessile attached to the bottom of the abdomen, and 

 descending perpendicularly. The S. turgens of Phipps is 

 the type. 



GENUS SYDNEUM. 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. 



GENUS POLYCLINUM. 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. 



(b.) Systems destitute of the central cavity, and the an- 

 gles of the branchial meshes without papillae. 



