REPORT ON THE TUNICATA OP PLYMOUTH. 75 



the resemblances between Diazona and Tylobranchion, the latter being 

 one of the most interesting of the " Challenger " forms make known to 

 us by Professor Herdman's researches. As I gather from Prof. Herd- 

 man's remarks upon Lahille's system of classification, this zoologist 

 groups together, along with Diazona and Tylobranchion, the genera 

 Ecteinascidia, Rhopalcea, and Giona. I believe, however, that Ectein- 

 ascidia is much more closely related to Sluiteria than to any of these 

 genera, and while Roule has established the relationship of Rhopalcea 

 and Ciona beyond doubt, the equally close affinity of Diazona to these 

 forms is still a matter of some uncertainty. That the mere formation 

 of a huge common mass of test enclosing the abdominal regions of the 

 zooids is not of itself a point of great systematic importance is 

 demonstrated by Pycnoclavella, which is in every other structural 

 respect a true Glavelina. Therefore on this head I am quite in accord 

 with Lahille in his efforts to break up the group " Ascidia? compositee," 

 and to classify the Ascidians upon morphological grounds only or in the 

 main. Yet I cannot but regard the definite position of Diazona and 

 Tylobranchion among the Cionidee as too forcible a disregard of the ties 

 which also bind them to the Polyclinidas and Distomidse. 



4. Diazona,* Savigny. 



Diazona, Savigny. Tableau systetnatique, 1. c, pp. 174, 175. 



— Dujardin, in Lamarck. Hist. Nat. des Anim. sans Vertebres, 



2nd ed. (par Deshayes and M. Edwards), t. iii, 1840, 

 pp. 498, 499. 

 Syntethys, Forbes and Ooodsir. On some Remarkable Marine 

 Invertebrata new to British Seas, Trans. Roy. Soc. 

 Edin., xx, 1853, p. 307. 



— Forbes and Hartley, Brit. Moll., iv, p. 244. 



Diazona, Alder. Observations on British Tunicata, Ann. and Mag. 

 of Nat. Hist, (iii), xi, 1863, p. 169. 



— Lahille. Comptes Eendus, cii, 1886, p. 1574, and civ, 1887, 



p. 240. 



— Giard. Comptes Rendus, ciii, 1886, p. 755, 756. 



— B. von Drasche. Die Synascidien, p. 8. 



— Cams. Prodr, Faun. Med., 2, ii, p. 480. 



* I greatly regret that my efforts to obtain a copy of Delia Valle's Con- 

 tribuzioni have been unsuccessful up to the time of going to press, and I 

 must express the same regret with regard to Lahille's Rechercbes sur les 

 Tuniciers. 



