REPORT ON THE TUNIOATA OF PLYMOUTH. 59 



Peeophoea Listebi, Serdman. Second Report, Proc. Biol. Soc. Liverpool, 

 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 papillae. 



Musculature feebly developed ; transverse fibres few, widely 

 separate from one another, extending from the dorsal region to the 

 middle of each side ; also forming a weak sphincter round each 

 aperture ; longitudinal fibres almost as well developed as the trans- 

 verse, extending from the oral sphincter as far as the level of the 

 first interserial bar of the bi'anchial sac ; several longitudinal fibres 

 arising anteriorly between the oral aperture and the anterior end of 

 the endostyle, extending with the longitudinal fibres of the oral 

 sphincter to the same distance ; longitudinal fibres of the cloacal 

 sphincter short. 



Habits. — Attached to stones or algae in shallow water. 



At Plymouth Perophora Listeri has been dredged in the estuary 

 of the Yealm, and in 4 to 5 fathoms water off the Duke Rock. 

 Mr. Heape recorded it as abundant on the rocks below the Hoe. 



There can be very little doubt that the name given by Wiegmann 

 to Lister's Perophora has been also applied to forms specifically 

 distinct from it. Lister, in his admirable paper, remarks upon the 

 existence of " finger-like processes, about eight in a row, that pro- 

 ject nearly at right angles into the central cavity '' [of the branchial 

 sac], and these are shown in some of his figures. 



Giard also mentions these papillte and compares them with the 

 papillae which were figured by Savigny in his account of Diazona 

 violacea. These papillae are simple and digitiform, so that Giard's 

 species probably did not differ from Lister's with respect to these 

 structures. 



On the other hand the species found at Naples and, as I gather 

 from Professor Herdman's paper, at Banyuls also (by Lahille) 

 present considerable differences from this simple arrangement. It 

 is probable, therefore, that Perophora Listeri does not occur in the 

 Mediterranean but is confined to the Atlantic shores of northern 

 Europe. 



The condition of the papillae in Plymouth specimens is shown on 



