REPORT ON THE TUNICATA OP PLYMOUTH. 71 



"rudimentary or imperfect internal longitudinal bars," but so far, I 

 believe, no perfect bars have been discerned in the branchial sac of 

 Perophora. In some specimens, however, sent to me from the 

 Zoological Station at Naples, aud labelled " Perophora Listeri " I 

 discovered some months ago that numerous perfect internal longi- 

 tudinal bars actually existed, being supported upon the ends of flat 

 triangular " connecting ducts " precisely as in Rhopalopsis crassa or 

 Ecteinascidia Moorei, with this difference only, that small papillse 

 were frequently present at the points of junction. The existence of 

 papillae on the bars renders the affinity between Perophora and 

 Sluiteria still closer than has been already believed. It is very 

 probable that a new species must be created for the Naples type, but 

 that is a matter to which I hope to refer in a subsequent paper on 

 the anatomy and variation of the genus. (See Postcript, p. 81). 



3. Perophora Listeri, Wiegmann. (PL II, figs. 4, 5, 6). 



Ascidia, sp., Lister. Phil. Trans., 1834, pp. 378 — 382, pi. xi. 



Peeophoea Listeri, Wiegmann. Archives, 1835, p. 309. 



Ascidia, n. sp., Fleming. Moll. Anim., 1837, pp. 202 — 209, pi. xvii, 

 fig. 59 (2). 



Peeophoea Listeei, Forbes and Hariley. L. c, p. 28, pi. E, fig. 2. 



— — Giard. Recherches, 1. c, pp. 615, 616, pi. xxi, 



figs. 3, 6 to 11, 13 to 15, pi. xxiv. 



— — Herdman. Second Eeport, Proc. Biol. Soc. Liver- 



pool, iii, 1889, p. 246. 



— — Herdman. On the Genus Ecteinascidia, 1. c, 



pp. 158—161. 



Zooids quadrangular, compressed from side to side, colourless, 

 transparent. 



Apertures widely separated, branchial with six lobes, cloacal with five. 



Tentacles forty in number, of three sizes. 



Branchial sac always provided with unbranched digitiform or 

 slightly triangular interserial papillae ; no rudiments of internal 

 longitudinal bars ; rudimentary horizontal membranes ; stigmata in 

 four transverse rows, two between each pair of interserial papillie. 



Musculature feebly developed ; transverse fibres few, widely separate 

 from one another, extending from the dorsal region to the middle of 



