TUN 1C AT A. 

 Fi. 770. 



1191 



Diazona violacea, magnified. (After Savigny.) 



circumscription ; animals sometimes scat- 

 tered, sometimes arranged in a quincunx ; 

 branchial orifice circular, without distinct 

 rays ; anal orifice very minute and indistinct ; 

 abdominal viscera pushed up by the side of 

 the thorax. 



Genus Leptoclinttm, Milne-Edwards. Com- 

 mon body sometimes coriaceous, sometimes 

 gelatinous, thin, sessile and incrusting ; sys- 

 tems few ; individuals arranged irregularly 

 around common cloacal cavities ; abdomen 

 peduncled, short, smaller than the thorax. 



The tribe Botryll'ma (Ics Botrylliens, Milne- 

 Edwards) comprises those compound Asci- 

 dians that are united in systems around common 

 excretory cavities or cloaca?, and whose bodies 

 are not divided into a distinct thorax and 

 abdomen, the viscera being pushed forward 

 on the side of the branchial cavity, and form- 

 ing with the thorax an ovoid mass. 



"Genus Botryllus, Gaertner ; synonyms, Al- 

 cyon'ntm, Auct., Polycyclus, Lamarck. Com- 

 mon body gelatinous or cartilaginous, sessile 

 and incrusting ; systems numerous, pro- 

 minent, round or star-shaped, with central 

 cavities ; individuals, six to twenty in each 

 system, lying horizontally with the vent far 

 from the branchial orifice; branchial orifice 

 simple (fig. 771.). 



Genus Botrylloides, Milne-Edwards. This 

 genus resembles the foregoing in most respects, 

 except that the stars formed by the systems 

 of animals are irregular and ramifying ; the 

 cloacae being prolonged into the common 

 mass as irregular internal channels, on each 

 side of which the individuals are placed in 

 linear series, instead of having a simple star- 



ce arrangement around the cloaca?, as in 

 tryllu*. The animals of Botrylloidcs, more- 



/er, have a nearly vertical position, and their 



ifices are closely approximate (Jig- 783.). 

 We should perhaps also refer to the group 

 the Botryllidce, an obscure form, first no- 



ticed by Molina*, and subsequently named 

 Pyura by Blainville, and considered by the 

 latter to form a link between the simple and 

 compound Ascidians. M. Blainville gives the 

 following characteristics. 



Fig. 771. 



Botrylh 



viofaccns. Two of (he star-tike systems, mag- 

 nified. ( After Milne- Edwards. ) 



n, a, common test ; b, b, b, some of the branchial ori- 

 fices ; c, the common anal orifice of one of the systems. 



Genus Pyura y Blainville. A pyriform body, 

 with two small short tubes, occupying a cell 

 in the external envelope, and forming, by its 

 union with 10 to 12 individuals, a kind of poly- 

 morphous mass somewhat resembling honey- 

 comb, apparently without any external orifice. 



* Saggio sulla Historia naturale del Chili, 

 logna, 1782, 4to. 



4c 4 



Bo- 



