MOLLUSCA. 151 



59. C^siRA. Meshes of the branchiae interrupted by 

 the folds. C. Diana of Sav. Tab. vii. f. 1. The Ascidia 

 qnadridentata of Forskael. 



(B). Tentacular filaments of the branchial orifice simple. 



The folds of the branchiae eight in number, four on each 

 side, and the meshes uninterrupted. Intestine strengthened 

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

 absent or indistinct. 



60. Styela. Ovarium divided, one division at least on 

 each side. S. Canopiis. Sav. Tab. viii. f. 1. 



61. Pandocia. Ovarium single, and situate in the fold 

 of the intestine. The Ascidia conchilega, a native species 

 is the type. 



2. Apertures xoith indistinct rays, or more than Jour. 



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. 



62. Clavelina. Branchial and anal orifices without 

 rays. Angles of the branchial meshes simple. Intestine 

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

 A. lepadiformis of MuUer belong to this genus ; the latter 

 of these is now recorded as a British species. 



h. Body sessile. 



The branchial orifice with eight or nine rays, and the 

 anal with six. The angles of the branchial meshes with 

 papillae. No liver. A cylindrical rib extending from the 

 pylorus to the anus. 



