Dr. W. A. Ilerdman on Diazona and Sjntetliys. 165 



XIX. — Note on Diazona and Syntethys. By W. A. Herd- 

 man, D.Sc, Professor of Natural History in University 

 College, Liverpool. 



Mr. W. Garstang has lately drawn attention, in his " Eeport 

 on the Tunicata of Plymouth " *, to the interesting point that 

 the Syntethys hehridicus of Forbes and Goods ir has been 

 considered by recent authors, on insufficient evidence, to be 

 the same as Diazona violacea, Savigny, and that therefore it 

 is possible that these two forms may be, if not distinct genera, 

 at least distinct species. 



The history of the matter is briefly as follows : — 

 Savigny, in 1816, described and figured f Diazona violacea 

 from Mediterranean specimens found at the Balearic Isles, 

 and established the genus Diazona^ which he placed, in his 

 * Syst^me des Ascidies,' at the head of the Tethyes composees 

 immediately after the genus Clavelina. Amongst other 

 points he describes and figures the colour as violet, the 

 branchial and atrial apertures as being both distinctly six- 

 rayed, the internal longitudinal bars of the branchial sac as 

 bearing papillee, and the meshes as containing each four 

 stigmata. 



Savigny was quoted and copied by various authors ; but 

 nothing of importance for tlie present purpose was added until 

 1851, when Forbes and Goodsir, in their paper " On some 

 remarkable Marine Invertebrata new to the British Seas" \, 

 described under the name of Syntethys hehridicus some speci- 

 mens dredged in 30 fathoms close to Crouliu Island, near 

 Applecross, on the west coast of Scotland. They recognized 

 the affinity of their new genus to Savigny's Diazona, and 

 placed it between that genus and Clavelina. They point out 

 that their species is of an apple-green hue, that the branchial 

 and atrial apertures are not lobed (although the atrial has six 

 white ocelli), that the ascidiozooids are marked by lines of 

 white pigment, that the branchial sac has thirteen rows of 

 stigmata, hooked fleshy tubercles at the angles of the meshes, 

 and only one of the stigmata in each mesh. Forbes and 

 Goodsir state as the characters distinguishing Syntethys from 

 Diazona (1) the simple apertures and (2) the sessile abdomen; 

 but, as Garstang has pointed out, the above details of struc- 

 ture of the branchial sac do not agree with those given by 

 Savigny for Diazona. 



* Journ. Mar. Biol. Assoc, n. s., vol. ii. no. 1, p. 47 (May 1891). 

 t Mem. pp. 35, Gl, 110, pi. ii. Hg. 3, and pi. xii. ; Syst. p. 174. 

 j Trans. Koy. Soc. Edinb. vol. xx. pt. ii. p. 307. 



