Mr. J. Alder on the British Tunicata. 1 69 



Diazona Hebridica, Forbes & Goodsir. 



Syntethys Hebridicus, Forbes & Goods, in Trans. Rov. Soc. Edinb. vol. xx. 

 p. 307; Forbes & Hani. Brit. Moll, vol/iv. p. 244. 



That the Syntethys Hebridicus of Forbes and Goodsir is really 

 a Diazona will be obvious to any one who has the opportunity 

 of carefully investigating its characters, one or two of which 

 appear to have escaped the observation of the distinguished na- 

 turalists who first described it. The division of the apertures 

 into six lobes is very difficult to make out, except in well-pre- 

 served specimens; and the elongated and pedunculated form 

 of the abdomen is a character varying exceedingly according to 

 the degree of contraction in which the animal is seen. I was 

 so fortunate as to dredge large masses of this remarkable Asci- 

 dian at Guernsey in 1853, and had the opportunity of examining 

 it in a living state, when it was at once recognized as the Syn- 

 tethys Hebridicus of Forbes and Goodsir ; but on placing speci- 

 mens in spirits, the apple-green colour of the living animals 

 began to change into a delicate violet, and the whole put on the 

 appearance of Diazona violacea of Savigny. This author, whose 

 anatomical details are admirable, has failed to give a good general 

 representation of the animal, from having had access only to 

 spirit specimens. His generic and specific names are in conse- 

 quence somewhat of misnomers, as the flattening of the surface, 

 from the individuals falling from the centre in dying, gives more 

 of a circular arrangement than really exists in nature. 



The change of colour has already been remarked upon. The 

 question arises, therefore, whether Diazona violacea and Syn- 

 tethys Hebridicus are not one and the same animal. The only 

 difference I can find is that the papilke of the branchial sac in 

 the latter are stout and obtuse, very different from the slender, 

 pointed form represented by Savigny; I have therefore deter- 

 mined to consider them distinct until further observations decide 

 the point. Prof. Goodsir has kindly supplied me with a portion 

 of a specimen from the original habitat, and, I believe, coincides 

 in the view of its generic relation here taken. I am also in- 

 debted for specimens to Mr. M 'Andrew. 



Its vitreous transparency and the opake white lines of the 

 thorax give this remarkable species very much the appearance 

 of a huge group of Claveliuce cemented together at the base. 



Poiyclinum succineum, n. sp. 



Common body subglobose, a little depressed, very transparent, 

 amber-coloured, attached by a broad base, the surface slightly 

 lobated. Individuals disposed over the surface without apparent 

 order, forming numerous systems, each with a prominent funnel- 



Ann. fy Mag. N. Hist. Ser. 3. Vol. xi. 12 



