268 Messrs. J. Wood-Mason and A. Alcock on 



ColeUci) and the Clavelinidas (s. str.). Hitherto no true"^ 

 Distoraid has been known to possess free zooids — that is, 

 zooids not completely imbedded in a common test. This new 

 Ascidian, however, combines the structural characters of the 

 Distomidje with a social form of colony which is only slightly 

 removed from that of the Clavelinida?. 



Further, Archidistoma aggregatum is of especial interest 

 because it exhibits the first stage in the evolution of the 

 coenobitic type of colony from the social Ascidian type, in 

 which the zooids are entirely free and irregularly placed : in 

 Archidistoma aggregatum, the clumps of zooids (primitive 

 ccenobia) have no common cloaca, but the cloacas of the indi- 

 viduals are usually situated towards the centres of the groups. 

 The second stage is exhibited in such a Compound Ascidian 

 as Synoicum turgens or Circinalium concrescens, in which 

 each of the isolated clumps of zooids possesses a common 

 central cloaca. 



XXXII. — Katural History Notes from H.M. Indian Marine 

 Survey Steamer ' Investigator,^ Commander R. F. Hoskyn, 

 B.N.y commanding. — Series II., No. 1. On the Residts of 

 Deep-sea Dredging during the Season 1890-91. By J. 

 Wood-JMason, Superintendent of the Indian Museum, and 

 Professor of Comparative Anatomy in the Medical College 

 of Bengal, and A. Alcock, M.B., Surgeon I.M.S., Sur- 

 geon-Naturalist to the Survey. 



[Continued from p. 138.] 



Class ASCIDIACEA. 



Family Cynthiidae. 



CuLEOLUS, Herdman. 



1. Culeolus sp. prox. recumhens, Ilerdman. 



Eight specimens of varying sizes from Station HO, 1997 

 fathoms, come very close to this species from the higher lati- 

 tudes of the Southern Ocean, if they are not identical with it. 



These are the only specimens of Tunicata that we have as 

 yet obtained from the deep sea. 



• The position of Chondrostachys is uncertain, but its nearest affinity 

 seems to be with Stereoclavella rather than witli O.iycort/nia. Diazona is 

 separated from the Distomidne by the pn>sence of iutemal longitudinal 

 bars in its branchial sac. 



