MOLLUSCA. 213 
Genus AuLpriprumM.—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, pla- 
ced at the bottom of the abdomen, and prolonged perpendi- 
cularly. Savigny divides the genus into two tribes. In the 
first, the individuals are simply oblong, with an ovarium 
shorter than the body, as A. ficus (Aleyonium fieus, Linn.) 
In the second, the individuals are filiform, with an ovarium 
longer than the body, as A. effusum of Savigny, tab. xvi. f. 3. 
Genus Dipemnum.—Individuals in distinct systems. 
The thorax is short and subglobular. The abdomen in- 
ferior, pedunculated, and larger than the thorax. The anal 
opening is obscure. The ovarium is single, sessile, and 
placed on the side of the abdomen. D. candidum and vis- 
cosum, from the Gulf of Suez, are the only known species. 
2. Branchial Orifice simple. 
The species form a thin fleshy crust on stones and sea- 
weeds. The individuals are stellularly arranged in distinct 
systems. The branchial orifice is circular and undivided. 
The abdomen is sublateral, and fixed at the bottom of the 
branchial cavity. The intestine is small, and the anus in- 
distinct. The angles of the branchial meshes are without 
papillze. 
Genus Botryiius.—Systems furnished with a central 
cavity. The systems are prominent, and consist of one or 
more regular concentric rows. The ovarium is double, 
being attached to each side of the branchial sac. 
This genus is subdivided by Savignyinto Botryll stellati, 
and Botrylli conglomerati. In the first, where the indivi- 
duals are distributed in a single row, there are some species 
