312 MALACOZOA. APODA. HEf EROBRANCHIATA. 



by authors. M. Savigny lias instituted several sub- 

 generic groups, founded on differences of organization ; 

 and gives to the present group the name of Phallusia, 

 derived from Phallus, in allusion to the form of some 

 of the species, but objectionable for several reasons. As 

 the Linnsean generic name ought to be given to some 

 group of the series, I think it may as well be applied to 

 this. 



1. Ascidia Prunum. Plum-like Ascidia. 



External sac subovate, compressed, or diversiform, extensile, 

 but not capable of being much elongated, softish, rugose, 

 transparent, hyaline, with a tinge of blue ; the upper or bran- 

 chial aperture forming a hemispherical prominence, with eight 

 granulated papillae, separated by eight reddish rays ; the lower 

 aperture similar, with six rays ; the inner sac is oval, of a yel- 

 lowish colour; the intestine very wide, curved, its contents 

 dusky ; the ovary large, placed on one side, and of a yellowish 

 colour ; the branchial cavity extending to the end of the body ; 

 the upper prominence of the body communicating with the 

 external branchial aperture of a bright orange-red, as are the 

 parts around it, that colour extending downwards in streaks, 

 but not on the anal prominence. Length about an inch, 

 breadth a fourth less. 



Generally the external tunic is so transparent that the inter- 

 nal parts can be seen through it. It varies in form, being 

 oval, and sessile by a broad base, or oblong and somewhat 

 pedunculate. 



Common on dead shells, especially Cyprina islandica and 

 Cardium echinatum, from deep water off Aberdeen. Often 

 partially covered with Discorbis lobatulus. 



Ascidia prunum. Lamk. Syst. ; Ed. 2. iii. 529. Ascidia Pru- 

 num. Muller, Zool. Dan. 1, 42. PI. 34. f. 1, 2, 3. Pirena 

 Prunum. Flem. Brit. Anim. 468. 



2. Ascidia opalina. Opaline Ascidia. 



External sac suboval, or somewhat square, compressed, very 

 dense, cartilaginous, transparent, of an opaline-hyaline, or 

 bluish- white tint, its inner surface glossy and smooth. It is 

 terminated above by two, little-prominent, apertures, not far 

 distant from each other, the upper with eight radiating, irre- 

 gular, tuberculate lobes, the lower with six similar lobes. The 

 inner sac ovato-oblong, very thin, its upper half bright scarlet, 



