FAUNISTIC RESULTS. 447 



animals both on the oyster beds and on the sandy stretches between. The huge 

 black trepang, Holothuria atra, and the flat urchins, Clypeaster humilris and Laganum 

 depression, eat their way through the sand, and the star-fishes, Pentaceros lincki 

 (Plate I., fig. 1), Luidea maculata, and Astropecten hemprichi prowl over the surface 

 and devastate the pearl oysters. 



Amongst the worms, in addition to the numerous parasites that infest the oyster, 

 there are two abundant species of Polydora that call for special mention P. homelli, 

 found burrowing in the oyster shells, and P. armata, a commensal in the globular 

 scarlet sponge, Aulospongus tubulatus (Plate II., fig. 3). Polyzoa are especially 

 abundant, and are a factor of importance in the building up of the calcareous masses 

 on the reefs and the paars Schizoporella riridis may extend for several feet, and 

 Lepralia cucullata is abundant, encrusting oyster shells, ascidians, sponges, and 

 almost all other objects with its dark purple spots and patches. 



Crustacea of various kinds abound, but so many species are represented that there 

 seem to be no specially notable ones. The Alpheidse are common, Pagurids are very 

 abundant, and crabs, mostly of small size and many of them inconspicuous from their 

 protective shapes and colouration, are found in every haul of the dredge. 



In addition to common Gastropod and Lamellibranch shell-fish, there are sevei'al 

 Opisthobranchs notably Philine aperta and Aplysia cornigera that congregate in 

 great numbers in some parts of the Gulf of Manaar. Pinna is abundant in places 

 and of large size. Species of Pinaxia, Sistrum, Nassa, and Purpura are found 

 boring into the smaller pearl oysters, and the large " Chanks" (see Plate I., fig. 3, 

 A, B, C, D) are of importance both as damaging the large oysters and also as 

 constituting a fishery themselves. Modiolus barbatus (Plate I., fig. 2), from its habit 

 of weaving entanglements, is another molluscan enemy of the younger pearl oysters. 



The large simple Ascidian Rhabdocynthia pallida is abundant on some parts of the 

 Gheval Paar. Several species of Amphioxus burrow in sand, the commonest on the 

 Gheval and Periya paars being Branchiostoma lanceolatum, var. belcheri and 

 Asymmetron cingalense. Gver 200 species of fishes frequent the pearl banks, and 

 many of these are carnivorous, including especially the file and the trigger fishes 

 and the gigantic rays. In addition to the species that have been mentioned as 

 especially common, characteristic, or important, there are enormous numbers of the 

 smaller organisms belonging to many invertebrate groups that are found encrusting 

 and attached to the shells of the older pearl oysters. Fig. 7 on Plate II. shows a 

 photograph of such a "microcosm" from the Cheval Paar. 



Such are the animate surroundings, including both friends and foes, amid which 

 the pearl oyster habitually lives in the Gulf of Manaar, and seems, if left in comparative 

 peace, able to hold its own in the struggle for existence ; but the balance, as we have 

 shown in previous parts of this report, is liable to be seriously disturbed by three 

 all-powerful factors : devastating hordes of voracious fishes which come up from the 

 deeper waters and leave crunched shells and torn byssus in their wake ; storms, 



