304 CEYLON PEARL OYSTER REPORT. 



all of much the same size, hut every fourth one is in places wider than the three 

 intermediates and has a rather wider horizontal membrane. The papillae on the 

 rather narrow internal bars are large. They vary in length, but on the average 

 extend about half-way across the mesh. 



Dorsal Lamina a wide membrane with well-marked shelf-like ribs, and marginal 

 points (fig. 6). The ribs die away as they approach the free edge. 



Tentacles numerous and rather slender, 50 to 60, larger and smaller, but none very 

 small (fig. 9). 



Dorsal Tubercle large, cordate in outline, with the posterior end pointed, the 

 opening anterior and both horns rolled inwards (fig. 4). 



The Viscera occupy the ventral half of the rather wide posterior end of the bodv 

 (fig. 3). The intestine is relatively wide. 



Locality : (l) Navakaddu Paar, Gulf of Manaar, 8 fathoms, 1 specimen ; (2) outer 

 Chilaw Paar, Station LXIX., depth 8 to 11 fathoms, 2 specimens; (3) Cheval Paar, 

 attached to oyster cages, 2 specimens. 



This species is described above from the single large specimen obtained on 

 Navakaddu Paar ; but the couple of Ascidians from Cheval Paar and those from 

 Chilaw Paar are probably also specimens of the same species. They have not all the 

 same external appearance, but the internal organisation appears to correspond fairly 

 well. One of the larger specimens is partly overgrown by a colony of Botrylloid.es, 

 and that may account for some difference in shape and appearance, while a couple of 

 smaller specimens (1 centim. long) are probably young and still undeveloped. The 

 body of the larger specimen from Chilaw Paar when removed from the test is shown 

 in fig. 8. The siphons are especially long and are ridged longitudinally and provided 

 with slight tag-like processes of connective tissue. The muscle bundles are especially 

 prominent round the edges of the right side of the mantle. Fig. 9 shows the dorsal 

 tubercle and tentacles of this specimen from Chilaw Paar. In the shape of the body 

 and especially in the long siphons, and also in the distribution of the muscle bundles 

 round the edges of the right side (fig. 8), this specimen recalls the " Ascidia canali- 

 culata (Heller)?," described by Sluiter, in 1885, from Billiton, which he later 

 (1898) decided to recognise as a distinct species under the name of Ascidia divisa 

 but differs markedly from that form in the structure of the dorsal tubercle. Nor 

 does it agree with the true A. canaliculata, Heller, as described by Sluiter and 

 others ; nor yet with A. hisulca, Sluiter, which it resembles superficially, but differs 

 from in the details of the branchial sac and dorsal lamina. The species to which it is 

 most nearly related is Ascidia loiu/itubis (Traustedt) from the West Indies. The 

 agreement extends to the body form, the musculature, and the dorsal tubercle ; but 

 the two species differ in the details of the branchial sac. It is possible, however, that 

 several of these species which have been mentioned above may come to be united 

 when a larger range of specimens and of variations have been studied. 



This new species is named in honour of Captain Donnan, C.M.G., for many years 



