286 DE. W. A. HERDMAN ON BRITISH TUNICATA. 



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

 tudinal bars strong and numerous, bearing large irregularly 

 shaped 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 obliqtta, Alder. (Plate XVIII. fig. 3.) " 



Ascidia obliqua, Alder, Ann. 8f Mag. JS 7 at. 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. Sars ; 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- 

 gitudinal bars thin but distinct, bearing papillae at the corners of 

 the meshes ; these papillae 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 depressa, Alder 8f Hancock. (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 Uanley, British Mollusca, vol. ii. p. 373 (1853); Alder, 

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

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

 10-12 (from Denlcsch. d. k. Akad. d. Wiss. Bd. xxxiv., Wien, 1874) 

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



