ASCIDIA IXdlfXATA. 1U9 



surface, are some adherent particles of sand and shells, 

 which become accumulated towards the border of the 

 attachment. It is somewhat depressed, is attached by 

 the entire side, and there is an irregular, thin, marginal 

 expansion. The apertures are slightly tubular, with 

 smooth longitudinal folds or plaits ; the branchial, 

 being turned towards the free or upper side, is sub- 

 terminal : the anal is a little more than half way down 

 the ventral side. The blood-channels are of a pale 

 yellow colour, much branched and pretty-evenly dis- 

 tributed over both the external and internal surface of 

 the test. The main branches are large, and the ex- 

 tremities of the terminal twigs are rounded but not 

 enlarged. 



The mantle is narrower than the visceral mass and 

 projects very little backwards beyond it. The mus- 

 cular fibres are well developed, and are interwoven; 

 the longitudinal and diagonal ones are inconspicuous, 

 but the transverse are the most numerous and are 

 closely netted. The tubes are short, but rather wide ; 

 the anal, projecting from the ventral margin a little 

 more than half way down, is turned forward ; the 

 branchial is turned a little upwards or towards the 

 left side. 



The branchial sac (PL XVII, fig. 10), which, like the 

 mantle, is not so wide as the visceral mass, at least as 

 it appears in the contracted state, extends backwards 

 very little beyond the stomach. It is minutely plicated; 

 the primary vessels are rather distinct, nearly equal in 

 size, and regularly disposed; the stomata are rather 

 long, rectilinear, with the extremities usually a little 

 pointed. The papilla? of the intersections are large 

 and unusually long, with the sides almost parallel; 

 but are shouldered near the summit and have their 

 apices rounded. There are intermediate tubercles on 

 the longitudinal bars, which, though very much smaller, 

 are of the same peculiar form as the primary. The 

 papillary membrane is moderately developed. The oral 

 lamina is wide and strongly ribbed on the right side, 



