62 REPORT ON THE TtJNICATA OF PLYMOUTH. 



I gatliei' from Professor Herdman's remarks upon Lahille's system 

 of classification^ this zoologist groups together, along with Diazona 

 and Tylohranchion, the genera Ecteinascidia, Ehopalsea, and Ciona. 

 I believCj however, that Ecteinascidia is much more closely related 

 to Sluiteria than to any of these genera, and while Roule has 

 established the relationship of Rhopalsea 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 

 Clavelina. Therefore on this head I am quite in accord with Lahille 

 in his efforts to break up the group " Ascidiae compositas," and to 

 classify the Ascidians upon morphological grounds only or in the 

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

 Tylohranchion among the Cionidse as too forcible a disregard of the 

 ties which also bind them to the Polycliuidge and Distomidse. 



4. Diazona,"^ Savigny. 



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



— Diijardin, in Lamarck, Hist. Nat. des Anim. sans Vertebres, 2nd ed. 



(par Deshayes and M. Edwards), t. iii, 1840, pp. 498, 499. 

 Syntethys, Forbes and Goodsir. On some Remarkable Marine Invertebrata 



new to Britisb Seas, Trans. Roy. Soc. Edin., xx, 1853, p. 307. 

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



Diazona, Alder. Observations on British Tunicata, Ann. and Mag. of Nat. Hist. 



(iii), xi, 1863, p. 169. 



— Lahille. Comptes Rendus, cii, 1886, p. 1574, and civ, 1887, p. 240. 



— Giard. Comptes Reudus, ciii, 1886, pp. 755, 756. 



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



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



Colony gelatinous, sessile ; the zooids superior, their thoracic 

 portions freely projecting. 



Musculature with longitudinal fibres united into well marked 

 bundles. 



Branchial sac with festooned horizontal membranes, supporting 

 complete, rarely incomplete, internal longitudinal bars, not papillate at 

 the point of junction ; dorsal languettes triangular, compressed from 

 before backwards. 



Genitalia in the loop of the intestine ; oviduct (always ?) and vas 

 deferens present. 



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

 been unsuccessful up to the time of going to press, and I must express the same regret 

 with regard to Lahille's Recherches sur les Tuniciers. 



