180 ME J. D. MACDONALD ON THE REPRESENTATIVE 



dredged up in deep water in Bass Strait. The particulars of its anatomy, witii 

 several figures, were published in the Ann. and Mag. Nat. Hist, at the time ; and 

 it has since been obtained by Mr F. N. Raynek, R.N., late surgeon of H.M.S. 

 " Herald," in the neighbourhood of Torres Strait. It may be remarked, that the 

 whole mass is quite colourless and pellucid, but in other respects it is sufficiently 

 described in the table. 



Diazoiia. 



It has often appeared to me that Diazona was more closely related to the 

 Social than to the Compound Tunicata, from the similarity of its structure to that 

 of Syntethys. The position assigned to it in the table is quite in accordance with 

 the definitions there given. 



Diplosoma (milii). 



This genus I have found both in the S.W. Pacific and in the West Indies. 

 The mass is gelatinous and filmy, and the thorax in the zooids is double — a con- 

 dition that may be traced even long before the young escapes from the ovum. It 

 was described and figured in the Transactions of the Linnean Society as the 

 first step towards the still more paradoxical development of the ovum in Bo- 

 tryllus and Pyi'osoma. 



Syncecium and Sidnyum. 



Though certain general considerations have induced me to place these genera 

 near the true Botryllians, I cannot yet say whether they have an inter-communi- 

 cating palliovascular system or not ; and as it would be equally wrong, should 

 such be the case, to place them anywhere else, they may remain where they are 

 until the question is settled, and the (?) is removed. 



Polyclinoides (mihi). 



I have applied this term to an Australian genus of compound Ascidians, dis- 

 tinguished from Botryllus by having a distinct abdomen, and the generative 

 organs pedunculated, forming a post abdomen, — and from Polyclinum, by possessing 

 a compound palliovascular system, and fewer zooids surrounding the cloacae ; 

 besides which the mass is thin and encrusting, as in Botryllus. The branchial 

 aperture is considerably elevated, and six-lobed. The superior margin of the 

 cloacal opening is much produced, and three-lobed at the extremity, which is 

 simple in Botryllus. 



Pyrosomopsis (mihi). 

 A name which I have applied provisionally to a curious genus of Salpians, in 



