76 CEYLON PEARL OYSTER REPORT. 



pointed ; front of cladome flattened. A specimen from a boiled-out preparation, 



somewhat longer than usual, gave the following measurements: Shaft, 1'96 millim. 



by 0-019 millim. ; cladi, 0-0656 millim. by 0'0i64 millim. 



(3.) Oxea (Plate II., fig. 5,f); fairly stout, fusiform, gradually and usually fairly 



sharply pointed, gently curved, approximately iso - actinate, measuring about 



1-3 millims. by 0-032 millim. 



(4.) Chiasters (Plate II., fig. 5, <j, h, i) ; with no centrum and very slender, slightly 



roughened and distinctly tylote rays ; total diameter of spicule up to about 



- 02 millim. ; abundant, especially in the deeper parts of the sponge. 



The histological structure of the strongly developed cortex agrees very closely in 



some respects with that described and figured by Sollas (loe. cit., p. 122) for his 

 Piloelirota pachydermata. The cortex itself, about 0'8 millim. in thickness, consists 

 chiefly of very dense fibrous tissue, in which the fibres interlace in various directions. 

 Imbedded in this tissue we find histological elements of two other kinds : (l.) Large, 

 rounded, deeply staining bodies up to about 0'2 millim. in diameter, each made up of 

 an aggregation of much smaller bodies (cells ?), and the whole very finely and 

 uniformly granular. These remarkable bodies have a rather deep yellowish brown 

 colour in unstained preparations, and they form a single layer beneath the surface in 

 the outer part of the cortex. They are evidently homologous with what Sollas 

 terms " oval or round clusters of granule-cells" in P. pachydermata. Sometimes the 

 finely granular " cells" occur separately as well as aggregated in clusters, especially 

 in the margin of the vent. (2.) Numerous irregularly scattered, small groups of 

 faintly staining, homogeneous, spherical globules, varying in size in each group up to 

 about 0'005 millim. in diameter; abundant in the deeper parts of the cortex and also 

 in the choanosome. These bodies do not seem to have been observed in P. pachy- 

 dermata. 



Beneath the fibrous cortex lie extensive sub-cortical crypts, separated from one 

 another by the radiating spicule bundles and a sparse development of ectosomal 

 collenchyma. 



The inhalant pore-sieves overlie well-developed chones which penetrate the fibrous 

 cortex to reach the sub-cortical crypts, being provided with sphincters or diaphragms 

 where they join the latter ; the sphincters, however, do not lie quite so deeply as the 

 lower limit of the fibrous cortex. From the sub-cortical crypts originate numerous 

 fairly wide incurrent canals which penetrate the choanosome and sub-divide therein. 



The choanosome is finely granular, and the flagellate chambers are approximately 

 spherical, about 0'02 millim. in diameter, and appai'ently eurypylous. 



It is not impossible that this species may be identical with Sollas's Piloelirota 

 cingalensis, also from Galle, but the description of the latter (15), apparently based upon 

 a mere fragment, for the author says " Sponge (?)," is too imperfect for safe 

 recognition. Sollas, moreover, states that the cortex is thin, about 0'35 millim. in 

 thickness, and all the megascleres seem to have their shafts characteristically bluntly 



