446 "CEYLON PEAKL OYSTER REPORT. 



derived from the disintegration of the granitoid rocks of Ceylon it is mainly 

 Foraminifera and shell fragments. The large amount of a few species of Foraminitera 

 in some deposits is a notable feature, which has been already discussed above. In 

 some parts, as on the South Cheval, balls of Lithothamnion fruticulosum, large and 

 small, are very abundant and are useful as cultch for the pearl oyster. 



Sponges are a very dominant group, and probably exercise considerable influence 

 upon the welfare of the oyster beds. The most important in this connection is Cliona 

 margaritiferce, the ravages of which have been described and figured in previous 

 sections of this report. Other characteristic forms are the large black Spongionella 

 nigra and the four species of Sponge shown on Plate II. Fig. 1 is the huge crater- 

 like Petroda testudinaria which occurs on the Cheval and especially on the Periya 

 Paar. Fig. 2 shows the two characteristic forms, the cup-like and the flabellate, of 

 Phakellia donnani, a brick-red Sponge found in great abundance on many parts of 

 the pearl banks, but especially on the Modragams, the Cheval, and the Periya Paar. 

 Fig. 3 is the scarlet spherical mass Atdospongics lubidatus, a Sponge in which the 

 minute Polycluete worm Polydora armata lives as a commensal. Fig. 4 is the 

 remarkable " umbrella " Sponge, Phyllospongia holdsworthi, which is said by the 

 divers to be characteristic of the " Koddai Paar" to the west of the Cheval. It is, 

 however, found also on various parts of the Cheval, Muttuvaratu, and Periya paars, 

 and elsewhere. 



Amongst Coelenterates, corals are the most conspicuous and important forms. 

 Living reefs composed of many common species compete successfully with the pearl 

 oysters at many places and prevent the formation of beds, while solitary forms such 

 as Fungict are found alive scattered over the sandy bottom on the Cheval and other 

 paars. In some places there are great aggregations of Heterocyathus aequicostatus 

 and Heteropsammia michelini, both of which have in their base commensal species of 

 Aspidosiphon and of Jousseaumia. Many of the reef-building corals, such as species 

 of Madrepora, Purites, Pcecilopora, Montipora, Favia, Goniastrea, Galaxea, and 

 Coeloria, are also found growing over the shells of living oysters. This is especially 

 the case on the Muttuvaratu Paar. Turbinaria cinerascens and T. crater are especially 

 common on some parts of the northern paars. 



Some of the fleshy Alcyoniidas are very common on the coral reefs at the pearl 

 banks, and form enormous colonies several feet in diameter. The Gorgonoid Alcyonaria 

 are for the most part found in deeper water outside the pearl-bank plateau, but 

 a few species such as Juucella juncea and Subcrogorgia suberotsa occur on the 

 Cheval Paar. 



One of the Hydroid Zoophytes, Campamdaria juncea, Allm., which grows to a 

 large size (Plate II., fig. 6), is especially characteristic of the East Cheval Paar. 

 Another handsome species from the pearl banks is Halicornaria insignis, Allm. 

 (Plate II., fig. 5). 



Some of the Ecliiuodermata are amongst the commonest and most conspicuous of 



