202 MOLLUSCA. 



ed by a cylindrical rib from the pylorus to the anus. Liver 

 absent or indistinct. 



GENUS STYELA Ovarium divided, one division at least 

 on each side. S. Canopus. Sav. tab. viii. f. 1. 



GENUS PANDOCIA. Ovarium single, and situate in the 

 fold of the intestine. The Ascidia conchilega, a native 

 species is the type. 



2. Apertures with indistinct rays, or more than four. 

 The external tunic is here soft, easily cut, and translu- 

 cent. The rays (when existing) of the branchial orifice 

 amount to eight or nine ; and those of the anal to six at 

 least. The branchiae are destitute of longitudinal folds. 

 The tentacular filaments of the branchial circle are simple. 

 Liver indistinct* Ovarium single. 

 a. Body pedunculated. 



The stalk is here placed at the base, and serves to sup- 

 port the body, being of an opposite character from that of 

 the Boltenia. 



GENUS CL.AVEIINA. Branchial and anal orifices with- 

 out rays. Angles of the branchial meshes simple. Intes- 

 tine destitute of a rib. The Ascidia clavata of Pallas, and 

 the A. lepadiformis of Miiller belong to this genus ; the 

 latter of these is now recorded as a British species* 

 As connected with this group the small Ascidia, figured 

 and described by Mr. Lister in the Philosophical Transac- 

 tions for 1834, deserves particular notice, as the following 

 important observations which he has recorded, sufficiently 

 indicate. They will indeed be perused with peculiar inter- 

 est by all who are practically engaged in the study of mol- 

 luscous animals. 



This compound animal occurs in groups that consist of 



