512 PHILOSOPHY OF ZOOLOGY. 



(A.) Tunic and branchial cavity straight 



63. PiRENA. The branchial sac as extended as the tu- 

 nic. Stomach not. resting on the intestine. P. Phusca of 

 FoRSKAEL is the type to which Savigny has added three 

 other species. The Ascklia prunum of Muller, a native 

 species, is probably of this genus. 



64. CiONA. Branchial sac shorter than the tunic, and 

 exceeded by the viscera. C Ascidia intestinalis, Lin. is a 

 native example of this genus. 



(B.) Tunic turned up at the base. 



65. Phallusia. Branchial sac extending beyond the 

 viscera into the pouch of the sac. Stomach resting on the 

 mass of viscera. The Ascidia mentula of Muller, a native 

 species, is the type. 



There is one genus, supposed to be nearly related to the 

 preceding, which is involved in great obscurity, the Bipa- 

 pilaria of Lamarck, which appears to be pedunculated, 

 with two apertures, each furnished with three setaceous 

 tentacula. 



B. Compound. 



The animals belonging to this division were formerly 

 included in the genus Alcyonium of Linnaeus, and placed 

 among the Zoophytes. They are compound animals, many 

 individuals united by a common integument, and arranged 

 according to a uniform plan. 



In some cases, there is only one system of individuals in 

 the mass, in other cases, there are many, similarly arran- 

 ged and contiguous. The tentacular filaments of the bran- 

 chiae appear to be distinct. They are destitute of the in- 

 testinal rib which occurs in some of the preceding genera. 



1. Bi-anchial orifice radiated. 



a. Branchial and anal orifices, with six rays. 



