600 PEor. w. A, heudman's eetised 



["Body divided into thorax, abdomen, and a well-marted peduncle. 

 7 \ Podoclavella. 

 I Body not pedunculated apart from the long abdomen 8 



i Stolons, and posterior end of body, united in a solid basal mass of 

 test Stereoclavella *. 

 Stolons distinct, delicate and branched Clavelina. 



DiAzoisrA t, Savigny, 1816. 



Colony massive, not pedunculated, consisting of a basal mass 

 of test surrounding the stolons and from which the ascidiozooids 

 project upwards. 



Ascidiozooids elongated, divided into thorax and abdomen, and 

 having the latter imbedded in the common basal mass of test. 

 Both branchial and atrial apertures anterior and 6-lobed. 



Test solid and thick in the lower part of the colony, thin and 

 delicate on the upper free parts of th.e ascidiozooids. Contains 

 numerous pigment-cells. 



Branchial sac large and well developed, with internal longi- 

 tudinal bars but no papillse. 



Dorsal lamina represented by triangular languets. 



Viscera extending far behind the branchial sac so as to form an 

 abdomen. 



Gonads in the intestinal loop. 



Three forms of Diazona have been described, whicli may be 



only varieties of one species, D. violacea, Sav. : — 



/ With no pigment-lines on thorax. B. intaota, Lah. (Med.) 



[ With white pigment-lines 1 



IWith pigmented circles round siphons, and inferior branchial circle. 

 D. violacea, Sav. (Med. & N.W. Eur.) 

 No pigmented circles round siphons, branchial circle superior. 

 D. hebridica, T. & G.| (N.W. Eur.) 



Ehopal^a §, Philippi, 1842. 



Sody elongated, divided by a constriction into two parts, 

 tliorax and abdomen. 



Test thick and cartilaginous. Branchial and atrial apertures 

 lobed. 



* Also Pycnoclavella, Garst. ; see p. 603. 



t This is the Syntethys of Forbes and Goodsir (1853). 



I Forbes and Goodsir, in their original description, say that tlie branchial 

 and atrial apertures are not lobed, while Alder states that they are obscurely 

 lobed. In B. violacea they are distinctly lobed. Forbes and Goodsir's figure 

 shows pigment around the atrial aperture. 



I The Ehopalona of Eoule and others. This form has afSnities with Ciona 

 and the Ascidiidse, but is, I consider, more closely related to the Clavelinidie. 



