342 3IANUAL OF THE MOLLUSCA. 



Tijpe, L, maculosum Edw. (L. gelatinosnm, F. and H. PL A, B, fig 5.) 

 Test coriaceous or gelatinous, thin, incrusting ; systems few ; individuals 



grouped irregularly round common doacal cavities ; abdomen pedunculate, 



short, smaller than the thorax. 



Bistr. Brit. 6 sp. On roots of laminariae ; in colour white, yellowish, 



or variegated with blue. 



Division h. Bi-stellate Didemnians. 

 DiSTOMUs, Gaertner. 



Efym. Bistomos two-mouthed. Syn. Polyzona, Mem. 



Ex. D. fuscusPl. 24, fig. 12, a detached zo'id. 



Test semi-cartilaginous, polymorphous, sessile : systems numerous, usually 

 circular ; individuals 1 or 2 ranked at unequal distances from their common 

 centre ; both orifices 6-rayed. 



Bistr. Europe, S. Africa, Australia. Brit. 2 sp. 



DiAZONA, Sav. 



Etym. JDia-zonai in circles. 



Ex. D. violacea, PI. 24, fig. 13 Medit. 



Test gelatinous, orbicular, sessile or somewhat pedunculate; tunicaries 

 very prominent, arranged in concentric circles on an expanded disk, fonn- 

 ing a single flower-like system; orifices 6-rayed; abdomen pedunculate; 

 ovary inclosed in the intestinal loop. 



Tribe 3. Polyclinina. 



Bivisio?i a, unistellate Polyclinians. 



POLYCLINUIJ, Sav. 



Etym. Polys many, Mine cavities. 



Ex. P. constellatum, PI. 24, fig. 15. 



Test gelatinous or cartilaginous, polymorphous, sessile or slightly pedun- 

 culate; systems numerous, convex, somewhat stellate, with central cloacal 

 cavities; tunicaries 10— 150, at very unequal distances from centres ; abdo- 

 men much smaller than thorax, post-abdomen pedunculate. 



Bistr. 6 sp. Brit., Medit., Red Sea, India. 



Aplydium, Sav. Sea-fig. 



Etym. Aploos simple. Ex. A. lobatum, PI. 24, fig. 14. 



Test gelatinous or cartilaginous, sessile; systems very numerous, slightly 

 prominent, annular or sub-elliptical, without central cavities ; tunicaries 

 (3 — 25) in single rows, equidistant from centres; branchial orifice 6-rayed ; 

 division of thorax and abdomen not always distinctly marked. 



Bistr. 6 sp. Eiu-ope, Red Sea. Attached to shells, &c., in deep water. 



