TUNICATA. 703 



A. Compound Ascidians. Common body gelatinous, or gela- 

 tinoso-coriaceous, polymorphous, often expanded, incrusting the 

 surface to which it adheres. 



Botryllus GARTNER. Body of the animalcules not distinguished 

 into thorax and abdomen ; branchial aperture circular without rays. 

 Several clusters of animals, each of them mostly stellate. 



Sp. Botryllus Schlosseri SAV., Alcyonium Schlosseri L., Botryllus stellatus 

 G.ERTN., PALL. Spic. Zool. x. Tab. iv. figs, i 5, SAVIGNY 1. 1. Tab. xx. 

 fig. 5 ; Botryllus polycyclus SAVIGNY 1. 1. Tab. iv. fig. 5, Tab. xxi. (re- 

 peated in GUERIN Iconogr., Mollusq. PI. 35, fig. i). In this and other 

 species every group has a common central cavity, into which the posterior 

 aperture of each several animalcule opens. In other species the several 

 animalcules are not placed circularly round such a cavity, and the two 

 openings of the body are closer together. The common mass is penetrated 

 by canals. Here belong the species which SAVIGNY refers to his first divi- 

 sion of Botryllus; MILNE EDWARDS forms of them, with the addition of 

 some new species first described by him, a separate genus under the name 

 of Botrylloldes, 



Didemnum SAV. (and Euccelium ejusd.) Common body sessile, 

 incrusting, without central cavity. Animalcules divided into two 

 separate parts, with branchial sac separated like a thorax from the 

 abdomen. Anal orifice without rays. Many groups of animals 

 collected in a common body. 



a. Branchial orifice ro tun date, destitute of rays. 

 Euccelium SAV. 



6. Branchial orifice with six equal rays or lobes. 

 Didemnum SAV., Didemnum and Leptoclinum MILNE EDW. 



Sp. Didemnum candidum SAV. 1. 1. PI. iv. fig. 3, PI. xx. fig. i, Cuv. R. 

 Ani., Moll. PL 129, fig. 3, &c. 



Polyclinum SAV. (and Aplidium ejusd.) Common body sessile, 

 polymorphous, often incrusting. Many groups of animalcules col- 

 lected together in a common body. Animalcules divided into three 

 separate parts, with ovary and heart behind abdomen contained in 

 the last part. Branchial orifice sexradiate; anal orifice without rays. 



Sp. Polyclinum constellatum SAV. 1. 1. PI. iv. fig. i, PI. xvm. fig. i, 



Iconogr., Moll. PI. 35, fig. 4; on the coasts of the island Mauritius; 

 Aplidium ficus SAV., Alcyonium jtcus L., ELLIS Corallines, PI. xvn. fig. 

 6. B, &c. 



