514 PHILOSOPHY OF ZOOLOGY. 



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

 descending perpendicularly. The S. turgens of Phipps 

 is the type. In the month of August 1817, we observed 

 at the Isle of May another species, adhering to a rock, and 

 differing from the turgens chiefly in the smoothness of its 

 skin. 



69. Sydneum. Anal orifice simple and tubular. 



The body is inversely conical. The stomach surrounded 

 with glands. Intestine spirally folded. Ovarium pedun- 

 culated. 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. 



70. Poi.YCLiNUM. Systems numerous, convex, stellular. 

 Individuals arranged irregularly round the common centre. 

 Abdomen inferior, pedunculated and less than the thorax. 

 Ovarium single, pedunculated, 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. 



(6.) Systems destitute of central cavity, and the angles 

 of the branchial meshes without papillae. 



71. Alpidium. Individuals in a single row round the 

 common centre. 



The thorax is cylindrical. The abdomen inferior sessile, 

 and of the size of the thorax. Ovarium single, sessile, 

 placed at the bottom of the abdomen, and prolonged per- 

 pendicularly. Savigny divides the genus into two tribes. 

 In the first, the individuals are simply oblong, with an ova- 

 rium shorter than the body, as A. Jicus {Alcyonkmi ficus, 

 Linn.). In the second, the individuals are filiform, with 

 an ovarium longer than the body, as A. effusuni of Savig- 

 ny, Tab. xvi. f. 3. 



