142 BRITISH TUX1CATA. 



the stomata rather large. The longitudinal bars are 

 not very stout and are further apart than usual ; and 

 there is, pretty-regularly, one to every plait. The 

 papillary membrane is well-developed, and has the free 

 margin thickened and arched ; and, as the thickened 

 portion projects a little from the bar, the latter seems 

 to be provided with small, obtuse papillae at their 

 intersections with the primary vessels. This, however, 

 is only a modification or rudimentary condition of the 

 ordinary branchial papillae. The oral lamina has on 

 the right side strong distinct ribs ; and the branchial 

 tubercle (PI. XX, fig. 11), at its anterior extremity, is 

 small and loop-formed with the points placed upwards 

 and turned to each other. The tentacular filaments 

 are numerous, long, slender, and variable in length, 

 and are placed very near to the anterior margin of the 

 branchial sac. 



The ovary is situated on the left side of the looped 

 portion of the intestine, and is composed of rather 

 delicate branches irregularly radiating from the centre; 

 occasionally a few ovarian branches appear at the 

 opposite side of the alimentary tube. The testicular 

 cceca are principally on the right side of the intestine. 



Professor Forbes has referred this species to the A. 

 prunum of Miiller, but we think erroneously. The A. 

 prnmnti is described as lax, hyaline, and very pellucid, 

 free or only slightly attached, dwelling in mud. This 

 species has the test rather coriaceous, and is always 

 firmly attached to stones throughout its whole length. 



28. Ascidia pellucida Alder & Hancock. 

 (PL XVI, figs. 8 and 9 ; PI. XVIII, fig. 12.) 



A*<: it'll jH-UiK-idu ALDER and HANCOCK in Trans. Tynesicle 

 N.F. Club, I [1848], p. 202; FORBES arid HANLEY Brit. 

 Moll. II [1849], p. 374. 



Body irregularly ovate or subtriangular, hyaline, 

 very much depressed, and attached by a thin, broadly- 



