SPONGES. 229 



The canal-system is typically leuconoid ; the flagellate chambers, abundantly 

 scattered in the ground-substance between the gastral and dermal cortex, being 

 spherical or sac-shaped, and having a maximum diameter of about 0'08 millim. The' 

 epithelial cells lining the larger canals contain numerous brown pigment granules. 



Spicnles. (1.) Dermal triradiates (Plate XIII., fig. 10, c, d) ; sagittal, with slender- 

 rays of not very unequal length, measuring, say, about 0'276 millim. in length by 

 G'016 millim. in thickness at the base, and tapering pretty gradually from base to 

 apex, which is sharp-pointed. The rays are all straight, and the angle between the 

 two paired rays is only slightly greater than the other two angles. 



(2.) Triradiates of the chamber-layer (Plate XIII., fig. 10, a, b) ; stout, sagittal, 

 with the basal ray somewhat shorter than the paired rays. liays usually straight ; 

 somewhat fusiform and gradually and very sharply pointed. Angle between paired 

 rays only slightly greater than the other two angles. The paired rays in a typical 

 example measured about 07 millim. in length by 0'066 millim. in maximum diameter, 

 with a basal ray about 0'57 millim. long and of about the same thickness as the 

 others. 



(3.) Gastral quadriradiates (Plate XIII., fig. 10, e, f) ; strongly sagittal, with the 

 paired rays extended nearly, or quite, at right angles to the conspicuously shorter 

 basal ray, and with the still shorter apical ray directed forwards almost in a line with 

 the basal. The rays are all straight, or nearly so, and only moderately stout, and 

 taper gradually from the base to the sharp-pointed apex. Length of paired rays 

 about 0'188 millim., with a diameter at the base of 0'012 millim. ; with basal ray 

 about 0'072 millim. long and apical ray about 0'048 millim. long; the basal ray of 

 about the same diameter as the paired rays ; the apical ray rather more slender. 



(4.) Fusiform oxea (Plate XIII., fig. 10, g); very slightly curved; gradually and 

 finely pointed at the inner end, but with the outer end nearly always broken off ; 

 moderately stout, measuring, say, about 074 millim. in length by 0'02 millim. in 

 maximum diameter. Arranged in sparse bundles at right angles to the surface, with 

 the outer ends projecting but slightly. 



This species is perhaps most nearly related to LENDENFELD'S Leucandra typica (79) 

 [= Leuconia typica, var. tuba, of POLEJAEFF (77)], from the East Coast of Australia 

 (and Bermudas ?), but differs considerably in details of spiculation. I have much 

 pleasure in naming it after Captain DONNAN, the veteran Inspector and explorer of 

 the Ceylon pearl banks. 



R.N. 186 (DONNAN'S Muttuvaratu Paar, Gulf of Manaar). 



FAMILY : AMPHOEISCIDA 



Heterocoela with a distinct and continuous dermal cortex. With conspicuous sub- 

 dermal quadriradiate spicules with inwardly directed apical rays. Flagellate 

 chambers varying from elongated and radially arranged to spherical and 

 irregularly scattered. 



