210 MOLLUSCA. 



tion of the branchiae, the circulation was distinctly visible 

 in the mantle near the openings, and the particles in the 

 blood were only of about the same size as above. 



b. 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. 



(A.) Tunic and branchial cavity straight. 



GENUS PIRENA. The branchial sac as extended as the 

 tunic. Stomach not resting on the intestine. P. phusca of 

 Forskal is the type, to which Savigny has added three other 

 species. The Ascidia prunum of Miiller, a native species, 

 may be referred to this genus. 



GENUS CIONA. Branchial sac shorter than the tunic, and 

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

 native example of this genus. 



(B.) Tunic turned up at the base. 



GENUS PHALLUSIA. Branchial sac extending beyond 

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

 the mass of viscera. The Ascidia mentula of Miiller, a na- 

 tive species, is the type. 



There are two genera supposed to be nearly related to 

 the preceding, which are involved in great obscurity. The 

 genus Bipapilaria of Lamark appears to be pedunculated, 

 with two apertures, each furnished with three setaceous 

 tentacula. The Mammaria of Miiller has only one termi- 

 nal aperture. One species inhabits the British seas. 



B. Compound. 



The animals included under this division were formerly 

 inserted in the genus Alcyonium of Linnaeus, and placed 



