DIAZONA VIOLACEA, SAVIGNY. 279 



amount of the blue puL-ple (indigo ?) dissolved in the yellow oil, and so 

 producing a greenish shade. Attempts are at present being made to 

 extract the colouring matter by Friedlander^s method and so prove its 

 <!heinic;il nature/' 



Dr. Holt proposes to publish a paper later on his chemical investigation 

 of these pigment changes. 



The fresh material has enabled me to make some further observations on 

 the arrangement of the ascidiozooids as seen in the living and expanded 

 colony. It is clear that, in some colonies at least, the ascidiozooids are not 

 placed evenly over the whole of the upper surface, nor are they scattered 

 irregularly, but are arranged in definite rows or groups with meandering 

 branching paths of smooth depressed test between. So that, looking at the 

 top of the expanded colony from above, one sees certain bare areas of test, 

 as shown in Plate 19. fig. 2. In all probability this grouping of the ascidio- 

 zooids is the result of lines of budding in the growth of the young colony. 

 In Alder and Hancock's 'British Tunicata ^ * the arrangement of the 

 ascidiozooids is described as " forming a single, irregular, or very indis- 

 tinctly concentric system '^ ; but there is no reason to regard this as Jbrming 

 a single " system," and the arrangement is certainly not concentric. 



In fig. 3, I show the arrangement of the " ocelli " or pigment spots in 

 relation to the branchial and atrial siphons and also the lines of snow-white 

 pigmentation on the thorax, as these structures are not represented correctly 

 in Forbes and Goodsir's figures. There are six ocelli at the atrial aperture 

 and none at the branchial, but a circle of white pigment spots, surrounds the 

 base of the branchial siphon, a short row of dots runs from this in the medio- 

 ■dorsal line to the nerve ganglion, a double line of white pigment bounds the 

 endostyle along the ventral margin of the branchial sac, and two parallel 

 white bands run along the dorsal edge of the thorax, terminating anteriorly 

 in a single row of white dots facing that of the ganglion on the opposite side 

 of the atrial siphon (see fig. 3). Each siphon terminates in six lobes. 



IV. The Systematic Position of Fosbesella tessellata (Forbes) . 



This West Coast species was first described by Forbes in 1848 f as Cynthia 

 tessdlata. Forbes's specimens were dredged by McAndrew in Mounts Bay, 

 Cornwall, from 25 fathoms, and the species has since been found in deep 

 water at several localities round the South and West coasts. In 1891, from 

 the examination of some specimens dredged off the west of the Isle of Man, I 

 drew attention to the fact that this species seemed to occupy an intermediate 

 position between the subfamilies Cynthiinse and Styelinse, agreeing with the 

 former in the compound tentacles and with the latter in having only four 



* Edited by Hopkinaon, Eay Soc, vol. ii. 1907, p. 159. 

 t British Mollusea, vol. i. p. 38. 



