748 Proceedings of the Royal Irish Academy. 



V. — The Pelagio Tunicata. By Professor W. A. Herdman, F.R.S., 



University College, Liverpool. 



Mr. E. T. Beowjste has asked me to examine a small collection of 

 Pelagic Tunicata wMch. he made at Valencia in the summers of 

 1895 to 1898. I have done so with much pleasure, hecause of the 

 special interest that attaches to the occurrence of the Salpidse and 

 Doliolidse in our seas. These forms do not, strictly speaking, helong 

 to the British fauna, but occasionally stray into our western waters 

 from their proper home in the Atlantic. Apparently at such times 

 the meteorological and other envii'onmental conditions, taken along 

 with the reproductive phase of the animal, conspire to bring an enor- 

 mous number of individuals of the one species into a limited area. A 

 typical case of this is seen in the remarkable shoal of Thalia democratica- 

 mucronata described in Mr. Browne's notes, as visiting Yalencia early 

 in September, 1896. Similar shoals of Balpa have been described 

 in the past by M'Intosh and others as occurring in the Outer 

 Hebrides. 



Salpid^. 



o 



Thalia democratica-mucronata, Porskal. 



(See Transtedt, Bidrag til Kundskab om Salpeme — Vidensk. Selsk 

 Ski\, 6te Raikke, 2 det. Bd. viii., p. 365; and " Challenger" 

 Eeport on Tunicata, Part iii., p. 79.) 



The solitary forms are especially large (up to 2 cm. in length), 

 larger than any collected during the " Challenger" Expedition, 

 and have the proliferous stolons, or " chains," very well deve- 

 loped. 



The aggregated forms show various stages in development, 

 and have their chains more or less broken up. Some indi- 

 viduals, not united in chains, are very large (up to 2 cm. in 

 length). These are preserved in formalin, and they show the 

 dilated form and watery consistency of the test better than any 

 of the specimens preserved otherwise ; but the muscle bands 

 and other internal tissues are not in such good histological con- 

 dition. 



