96 Dll W. A. HERDMAN ON 



rather than hemispherical in outline, the anterior end being truncated and 

 almost as broad as the base of attachment. The most projecting point of the 

 anterior end is placed midway between the two apertures, which are far apart, 

 and distinctly upon the right side of the extremity (see PI. XVII. fig. 5). Probably 

 on account of extreme contraction, they are also sessile, rather inconspicuous, 

 and irregularly lobed. 



The test is thick, strong, and leathery ; greyish- white on the outer surface, 

 and white in section. At the posterior end it has several root-like prolonga- 

 tions from 1 to 12 cm. in length. The mantle is thick, strongly muscular, and 

 closely united to the inner surface of the test. 



The branchial sac has eight very prominent folds, four upon each side. The 

 two dorsal folds on each side are more closely placed than the ventral ones, 

 and the clear spaces bordering the endostyle are considerably wider than those 

 beside the dorsal lamina. As the branchial sac of this species has never, so 

 far as I am aware, been figured, I give a view (PI. XVII. fig. 6) from the inside 

 of a part showing two folds and the interspace in their natural relations, while 

 at the right-hand side another interspace is represented as more exposed by the 

 removal of the next fold. The sac is a very thick one, the folds being prominent, 

 the internal longitudinal bars numerous, and the stigmata comparatively small. 

 Occasional wider transverse vessels occur ; in some places (see fig., tr) they 

 alternate regularly with three smaller ones {tr'). Delicate membranes dividing 

 the meshes are only present here and there (tr"). At the base of each fold 

 lies a series of large meshes (mh), each of which I found contained about 

 six stigmata. Heller mentions meshes with ten to twelve stigmata each ; I 

 found such only in the series adjoining the endostyle. 



The simple tentacles are numerous and closely placed. The dorsal tubercle 

 is small and nearly circular in outline, being slightly elongated laterally. The 

 aperture is anterior, and both horns are coiled inwards. 



The margin of the anus is expanded, and cleft into a number of blunt pro- 

 cesses. 



The yellow polycarps and grey endocarps are so numerous as almost com- 

 pletely to hide the inner surface of the mantle. 



Family Ascidiid^e. 



Ascidia tritonis, n. sp. (Plate XVI.). 



External Appearance. — Shape ovate, flattened laterally, attached by posterior 

 half of left side, especially towards the ventral edge ; anterior end rather 

 narrower than posterior but blunt. Dorsal edge slightly more convex than 

 ventral. Branchial aperture terminal, sessile, wide, lobes distinct. Atrial 



