298 CEYLON PEARL OYSTER REPORT. 



As an example of the number of Tunicata that live along with, and may be said to 

 infest, the pearl oyster, I give the following list of species found on examining the 

 oyster-cages suspended from the ship when on the Cheval Paar : Ascidia donnani, 

 Rhabdocynthia ceylonica, Diandrocarpa brakenhielmi var. ceylonica (many colonies), 

 Botryllus ater, Botrylloides chevalense (many colonies), Diplosoma gelatinosum, and 

 several smaller colonies of Leptoclinum, and other compound Ascidians undetermined. 

 In addition, many other species were found attached to and encrusting the pearl- 

 oysters on the bottom. Notable cases are Styela areolata, Rhabdocynthia pallida, 

 Psammaplidium ceylonicum, and Leptoclinum margaritifercp,. 



Even colonies attached to other objects on the bottom, such as the Leptoclinids 

 growing over the sand, must have their influence in competing for microscopic food, 

 and thus the fixed Tunicata may fairly be classed amongst the enemies of the pearl 

 oyster in the passive struggle for existence. 



DESCRIPTION OF THE TUNICATA. 



FAMILY: CLAVELINID^. 



Perophora hornelli, n. sp. Plate I., figs. 1 to 8. 



External Appearance. Small colonies of a few Ascidiozooids and buds each (fig. l), 

 attached to a slight stolon which is encrusted with sand (fig. 3). The atrial aperture 

 has five or six lobes (fig. 6). Colour, dull greenish brown (in spirit). Size, 4 millims. 

 in length by 2 to 2 '5 millims. in breadth. 



Test very thin. 



Mantle with numerous fine interlacing muscle bands, mostly transverse in direction. 



Branchial Sac with rather short wide stigmata (figs. 4, 5). Some parts of the sac 

 are papillated and others not. The papillae split at their ends and send prolongations 

 anteriorly and posteriorly to form incipient bars (fig. 5). In some parts of the sac 

 the bars are complete and bear small papillae (fig. 4). 



Dorsal Languets short and triangular in shape (fig. 8). 



Tentacles in three series (fig. 8). There are about 10 of each of the two larger 

 series. Those of the third, most anterior, series are very much smaller. 



Dorsal Tubercle, with a simple circular aperture (fig. 8). 



Alimentary Canal showing a simple stomach and several differentiated regions in 

 the short wide intestine (fig. 7). 



Locality : On Navakaddu Paar, in the southern part of the Gulf of Manaar ; 

 depth, 8 fathoms. 



This species agrees with VEBRILL'S Perophora viridis, from the East Coast of 

 North America, which is possibly the same as LAHILLE'S P. banyulensis from the 

 Mediterranean, in having the more or less complete system of internal bars in the 

 branchial sac shown in the figures (Plate I, figs. 4 and 5). 



