286 DE. W. A. HEEDMAN ON BEITISH TUNICATA. 



transverse vessels all one size, ratlier far apart. Internal longi- 

 tudinal bars strong and numerous, bearing large irregularly 

 sliaped papillae at the angles of the meshes, and smaller conical 

 intermediately placed ones. Meshes having the vertical extent 

 nearly twice as great as the horizontal, each containing two or 

 three stigmata. 



Dorsal lamina rather broad, strongly ribbed transversely, margin 

 plain. 



Tentacles rather large, placed close together, long and short 

 alternately, about 12 of each size. 



Olfactory tubercle simple, opening anterior, horns not coiled. 



Ascidia obliqtja, Alder. (Plate XVIII. fig. 3.) 



Ascidia obliqua, Alder, Ann. Sf Mag. Nat. Hist. 3rd ser. vol. xi. p. 154 

 (1863). 



In the collection at the Natural- History Eooms in the Edin- 

 burgh University there are two specimens of this species from 

 Lofoten, 300 fathoms, identified by Professor M. Sara ; they 

 agree perfectly with Alder's description of British specimens 

 (Lamlash). Those, on the other hand, described and figured by 

 Heller (Untersuch. &c, 1 Abth. p. 13, Taf. iv. fig. 5) are un- 

 doubtedly a distinct species. 



Alder gives a good description of the external appearance; an 

 account of a few points in the internal structure is still wanting. 



Branchial sac delicate, longitudinally plicated. Internal lon- 

 o-itudinal bars thin but distinct, bearing papiilse at the corners of 

 the meshes ; these papillss are rod-like in profile, but bear mem- 

 branous expansions, which are seen in the lateral view. Meshes 

 slightly longer vertically than transversely, each containing about 

 six elongated regular stigmata. 



Dorsal lamina transversely ribbed. 



Tentacles numerous, slender. 



Olfactory tubercle cordate. 



Ascidia depeessa, Alder SfHancoch. (Plate XVIII. figs. 4, 5.) 

 Ascidia depressa, Alder, Catalogue of the Marine Mollusca of North- 

 umberland and Durham, in Trans.Tynes. Nat. F. C. vol. i. p. 201 (1850); 

 Forbes and Hanley, British Mollusca, vol. ii. p. 373 (1853); Alder, 

 Hebrid. Invert., Brit. Assoc. Rep. for 1866, p. 208 (1867); Heller, 

 Untersuch. u. d. Tun. d. Adriat. u. Mittelm. 1 Abth. p. 15, Taf. v. figs. 

 10-12 (from DenJcsch. d. Jc. Akad, d. Wiss. Bd. xxxiv., Wien, 1874) 

 Macintosh, Marine Fauna of St, Andrews, p. 55 (1875). 



