PYHOSOMA. TUNIC AT A. 119 



b. Animals disposed in many concentric circles, forming the common mass. Gen. 



Diazoma. 

 * No particular systems formed by the disposition of the animals in the common mass. 



a. Two orifices, apparent externally, for each animal. Gen. Distomus, Sigillina. 



b. One orifice only, apparent externally, for each animal. Gen. Synoicum, JEucce- 

 lium^ Aplidium. 



Gen. 1. PYROSOMA, Lam. 



Animals biforous, aggregated, forming by their union a free, 

 floating, gelatinous, cylindrical, hollow mass, shut at one ex- 

 tremity, open at the other, and covered exteriorly with tuber- 

 cles ; orifices of the mouths exterior ; anal opening in the in- 

 ternal wall of the cavity of the mass ; two gemmiferous sacs, 

 opposite and lateral. 



The animals of this genus are gelatinous and transparent, and, placed horizontally 

 in the sea, appear capable of executing slight movements. They are very phosphores- 

 cent, and during the darkness of night often exhibit masses of floating light of the 

 most brilliant and varying colours. 



P. elegans, Lam. Body subconical, granulated, with tubercular 

 transverse bands ; tubercles naked, annulated. Inhabits Medi- 

 terranean sea Lam. iii. 111. 



P. gigantea, Lam. Body subcylindrical, with the tubercles unequal 

 and crowded, and the apex lanceolate. Inhabits Mediterranean 

 sea. Lam. iii. 111. 



Gen. 2. BOTRYLLUS. 



Aggregated biforous animals, adnate at the surface of a thin ge- 

 latinous, transparent crust, and composed of many orbicular 

 stelliform systems, each system disposed in a radiated form 

 round a central opening. Individuals ovoid, narrowed infe- 

 riorly, thickest and rounded at the summit, and perforated 

 above towards each extremity ; mouth near the circumference 

 of the cyst, with eight tentacula, of which four are larger than 

 the others ; anus near the centre ; two gemmiferous sacs. 



B. conglomerates, Pall. Gelatinous, convex, with conglomerate finger- 

 like divisions, and toothless terminal mouths. Inhabits British 

 coasts Fleming, 470. 



Gen. 3. POLYCYCLUS, Lam. 



Animals biforous, united in a common mass, gelatinous, thick 

 convex, fixed, the surface strewed with many-mouthed orbs, 

 with a cavity in the centre ; ten or twelve separate holes dis- 

 posed circularly around the cavity, with interior syphons com- 

 municating between these and the central opening. 



P. Renierii, Lam. Elongated, convex, attenuated, yellowish. In- 

 habits Adriatic sea. Mem. Mus. i. 340. 



Gen. 4. POLYCLINUM, Lam. 

 Animals aggregated, biforous, sunk in a gelatinous mass, flatten- 



