124 BBITISH TUNIOATA. 



being usually a bar corresponding to every second fold 

 of the respiratory membrane. The meshes formed by 

 the bars crossing the primary vessels are much wider 

 than long ; the papillae at the intersections are short 

 and obtuse and the papillary membrane is narrow. 

 The rectilinear stigmata of the secondary vessels are 

 rather long. The oral band is well developed, and is 

 for the most part smooth, but is imperfectly ribbed in 

 the vicinity of the mouth. The branchial tubercle 

 (PI. XX, f. 8) is rather large and strongly involuted, 

 and there are seventeen or eighteen moderately long, 

 equal, delicate, tentacular filaments a little above the 

 entrance of the branchial sac. 



The reproductive organs are placed on both sides of 

 the alimentary tube, but the ovary, which is a large, 

 dendritic and folliculate organ, is arranged round the 

 margin of the intestinal loop and sends ramifications 

 to both sides of it. The testicular caeca are of the 

 usual form, but are extremelv minute; thev are distri- 



e/ *- 



buted over each side of the intestine. The ras deferens 

 and oviduct are seen on the right side following the 

 contortions of the intestine, and both terminate close 

 to the anal orifice. 



-1. Ascidia obliqua Alder. 



(PI. XI, fig. 10; PL XVIII, fig. (3.) 



Axciilia olliqua ALDER in Ann. Nat. Hist. (3) XI [1863] , p. Io4. 



Body broadly ovate, light horn-coloured, rather 

 rugose when old, but not tuberculated, nearly smooth 

 when young, attached diagonally at the base and par- 

 tially at the side, leaning over towards the dorsal 

 aspect. Apertures not far apart, tubes conical, with 

 longitudinal grooves corresponding to the angles of 

 the lobes ; the branchial not quite terminal, the anal 

 median. Ocelli inconspicuous. 2W rather thin, trans- 

 parent, sometimes a good deal covered with zoophytes. 

 TentiirvJitr jilirnients slender. Bwncltiul sac with large, 

 subclavate, papillae. 0/v// linni/a transversely ribbed 



