REPORT ON THE TUNICATA. 1G9 



The Branchial Sac has four folds upon each Bide. There are three small transverse, 

 vessels between each pair of large ones. About eight internal longitudinal baxs are 

 usually present on the folds, and four in the interspace. The meshes are transversely 

 elongated and contain each nine to twelve stigmata. 



The Dorsal Lamina is narrow ; it is nut ribbed, and the margin is plain. 



The Tentacles are simple, filiform, and crowded ; there are about seventy, placed long 

 and short alternately. 



The Dorsal Tubercle is small and rudely circular in outline; the left horn is coiled 

 inwards, and the right outwards. 



This is a curious species; the shape is rather variable, as may be seen from the two 

 specimens figured (PL XXI. figs. 7 and 8). The dimensions given above are those of a 

 fairly large individual ; some of the specimens are much smaller. The body is more or less 

 globular, and the stalk is always very short. The apertures are slightly prominent and 

 very distinctly four-cleft (PL XXI. fig. 8), the branchial is nearly terminal and towards 

 the ventral edge, the atrial is on the antero-dorsal edge, about a quarter of the way 

 round it from the branchial aperture to the posterior end. Sand, mud and fragments of 

 shell adhere to the stalk and the posterior part of the body, and in some cases cover most 

 of the surface. Where not thus concealed by foreign bodies, the surface has a rich dark 

 green colour, the neighbourhood of the apertures being always the darkest part. 



The dark green test is closely united to the underlying mantle, which is also green. 

 Blood-vessels are very numerous on the test, and may be seen ramifying and anastomosing 

 freely (PL XXI. fig. 9, v.). Minute ovate or fusiform cells of a yellowish colour are very 

 numerous, scattered through the test matrix ; while in its inner part, below most of 

 the vessels, bundles of delicate fibres may be seen here and there, running in different 

 directions (PL XXI. fig. 9, /.); these do not belong to the mantle. The large dark- 

 coloured and mostly angular bodies, seen in fig. 9, are minute sand grains imbedded in the 

 test matrix. The epithelium (ectoderm) on the inner surface of the test is distinct. 



The branchial sac has four distinct folds upon each side, each fold having about eight 

 closely placed internal longitudinal bars (PL XXI. fig. 10, br.f.). In the interspaces 

 the bars are rather distantly placed, and consequently the meshes are large and contain 

 each usually ten or eleven stigmata. The arrangement of the transverse vessels — three 

 smaller ones alternating with two sizes of large ones — is very well marked and constant, 

 and all of them have undulating or jagged edges, which appear to be due to irregular 

 membranous expansions at their sides (I'l. XXI. tig. 10. tr., tr.' and tr."). 



Muscular fibres are present in all the vessels, and are arranged with great regularity. 

 The larger transverse vessels have two bands of fibres running along them, while the smaller 

 vessels have a single band each. Longitudinal bands are also present. Theselie intheinter- 

 stigmatic vessels, and each band forks as it crosses one of the larger transverse vessels, 



