REPORT ON THE TUNICATA. 217 



straight, while the dorsal is slightly concave. The body is attached by the posterior end 

 and the lower half of the left side. The apertures are both at the anterior end, they are 

 distinct, and the lobes are well-marked ; the branchial is towards the ventral edge, and 

 sessile ; the atrial is on the dorsal edge, forming a slight rounded projection. 



The surface is smooth, but slightly creased. The colour is a light yellowish-grey. 



Length of the body, 2 cm.; breadth of the body, 1*2 cm. 



The Test is of moderate thickness, it is transparent, and shows vascular ramification.-. 



Tlie Mantle has a well-marked musculature. 



The Branchial Sac is extremely delicate, and is not plicated. The vessels are all very 

 slender, and the transverse vessels are of much the same size throughout ; the internal 

 longitudinal bars are narrow, but well-marked, and have minute papillae at the corners of 

 the meshes, and connected by very narrow horizontal membranes. The meshes are nearly 

 square, the antero-posterior extent being generally slightly the greater. The stigmata 

 are long and narrow ; they are very regular, and are placed three or four in a mesh. 



The Dorsal Lamina is narrow, has a plain edge, and is scarcely ribbed ; at the base a 

 number of convoluted ribs commence, but they die out before reaching the edge. 



The Tentacles are filiform ; they are very long and numerous, with their bases almost 

 touching. 



This is a very elegant little species, it is well-shaped, stands erect, and is semi-trans- 

 parent. The projection of the atrial aperture causes a slight concavity in the dorsal 

 edge, and adds to the width of the blunt anterior end (PI. XXXIII. fig. 7). 



The branchial sac (PI. XXXIII. fig. 8) is very regular, and is the most delicate one 

 known in the genus Ascidia ; the stigmata are long and are closely packed, reducing the 

 transverse and fine longitudinal vessels to a very small size. Occasionally the stigmata 

 break through a transverse vessel for a short distance, and extend for twice the usual 

 length (see fig. 8, near i. I.). The internal longitudinal bars are slight, but distinct and 

 very straight. The papilla? at the angles of the meshes are minute but rather thick ; they 

 are connected by very narrow horizontal membranes, closely attached to the transverse 

 vessels. Occasionally very minute intermediate papillae are present on the internal 

 longitudinal bars for a few meshes ; they are also connected by fine horizontal membranes 

 (PI. XXXIII. fig. 8, tr.'), which span the uninterrupted stigmata, a fine transverse vessel 

 not being formed. 



The dorsal lamina is narrow, and has a plain edge (PI. XXXIII. fig. 9). A number 

 of ribs, commencing at the ends of the transverse vessels of the branchial sac, form 

 thickened convoluted bands on the inner part of the lamina, but they die out long before 

 reaching the- edge ; in some parts they are hardly so well marked as is represented in figure 9. 



In this specimen the entire lamina is distinctly marked by a network of capillary 

 ramifications, which are engorged with blood corpuscles of a reddish-brown colour; they 



