CATALOGUE OF TUNICATA. 11 



Ascidia incerta, n. sp., PL Asc. I., figs. 58. 



External appearance. The body is ovate, with very well-marked, 

 distinctly lobed siphons, upon which the apertures are placed. It is 

 attached by the posterior end. The branchial aperture is anterior, and 

 the atrial is about two-fifths of the way down the dorsal edge. The sur- 

 face is slightly rough and partly covered with adhering animals. The 

 colour is yellowish grey. Length 5 cm., breadth 3 cm., thickness 1'5 cm. 



Test thin, but tough, translucent; conspicuous vessels. 



Mantle fairly muscular round the edges of the right side, less 

 muscular in the centre of that side, and very thin and membranous over 

 the viscera. Siphons very distinct; branchial 7-lobed and atrial 6-lobed. 



Branchial sac minutely plicated, with transverse vessels all of one 

 size. Meshes nearly square, containing each about 7 stigmata. The 

 internal longitudinal bars bear at the angles of the meshes large curved 

 papillae, which vary a good deal amongst themselves in size and shape. 



The dorsal lamina is rather narrow. It is strongly ribbed, but has a 

 plain edge. The cesophageal aperture is fully two-thirds of the way down. 



The tentacles are very numerous, and closely placed. They are long 

 and slender, and differ somewhat in size amongst themselves, but there 

 is no regularity in their arrangement. 



The dorsal tubercle is simple but very large, occupying the whole of a 

 very deep peritubercular area. It is elongated antero-posteriorly, with 

 the horns curling outwards at the anterior end. 



Locality. Port Jackson. One specimen. 



This specimen from Port Jackson is in some respects very like 

 Ascidia pyriformis, found by the "Challenger" Expedition in the same 

 bay at a depth of 6 fathoms. I have given this species the specific 

 name incerta, because I still regard it as somewhat uncertain, or open to 

 doubt, whether or not it is distinct from A. pyriformis. In using the 

 dichotomising table of the characters of the species of Ascidia given in 

 rny " Revision, " at p. 591, one is led by the characters of the present 

 species straight to 'pyriformis at the top of p. 593 ; but on looking into 

 further details it is found that there are certain definable points of 

 difference. That being so, I think it wiser to describe A. incerta as a 

 distinct species ; but I think it quite possible that the examination of a 

 larger series of specimens than the 2 of pyrifonnis and 1 of incerta now 

 known, may lead to the union of the two species. The chief differences 

 are : the larger meshes of the branchial sac in A. incerta containing 

 7 stigmata (PI. Asc. I., fig. 6) in place of 3 or 4, the plain edge 'to the 

 dorsal lamina (fig. 7), and the remarkably large dorsal tubercle (fig. cS). 



