SPONGES. 163 



measurements which he gives of the spicules, whether his identification is correct ; 

 we have probably here yet another species of the genus. 



U.N. 220c (deep water off Galle and onwards up the West Coast of Ceylon). 



Paresperella bidentata, n. sp. Plate XL, tig. I. 



Sponge intensely arenaceous, the single specimen consisting of a friable mass of 

 coarse yellow sand, held together and permeated hy the soft sponge-tissues. Somewhat 

 cavernous internally. Surface uneven, with a soft dermal membrane visible in places. 

 The single specimen is an irregular massive fragment about 25 millims. in maximum 

 diameter. 



The main skeleton of the sponge, between the closely aggregated sand-grains, 

 consists of slender megascleres, mostly loosely scattered, but occasionally collected in 

 fairly stout multispicular fibres. In the dermal membrane there is a distinct but 

 very loose and wide-meshed reticulation of slender spicular fibre, three or four spicules 

 wide, supported here and there on very loose sub-dermal brushes belonging to the 

 main skeleton. 



Spicules. (1.) Tylostyli (Plate XL, fig. 1, a); long, slender, straight or nearly so, 

 with oval heads, about equal in diameter to the middle of the shaft, and slightly 

 constricted necks ; typically with the apex slightly enlarged, truncated, and provided 

 with two (sometimes three ?) minute conical teeth placed side by side on the truncated 

 end (with their long axes parallel with the long axis of the spicule). The enlarge- 

 ment from which these teeth project contains a diverticulum of the central canal of 

 the spicule. These spicules are best developed in the dermal membrane (and in the 

 lining membrane of the large canals ?). In the dermal membrane they form the 

 reticulation of spicular fibre mentioned above, and measure about 0"27 millim. by 

 0"0053 millim. In the deeper parts of the sponge, between the sand-grains, they are 

 more slender and their apices sometimes appear to end in simple, long-drawn-out 

 points. 



(2.) Palmate anisocheke (Plate XL, fig. 1, c, d), about 0'028 millim. long; mostly 

 in rosettes near the surface, very abundant and similar to those of P. serratohamata. 



(3.) Sigmata (Plate XL, fig. 1, b, b) ; long and slender, usually contort, with sharply 

 incurved apices and (? always) with more or less distinct teeth on the outer side of 

 each bend, similar to those on the sigmata of -P. serratohamata, but much less strongly 

 developed. Size about 0'052 millim. from bend to bend by - 002 millim. thick in the 

 middle. 



This species differs from P. serratohamata in the presence of two teeth, instead of 

 one, at the apex of the tylostyle ; in the much more slender and less distinctly toothed 

 or serrate character of the sigmata, and in the absence of toxa ; as well as in the 

 arenaceous habit, which has doubtless caused considerable reduction in the proper 

 skeleton. I know of no other case where one can trace such a close and evident 

 relationship between an arenaceous sponge with reduced skeleton and a non-arenaceous 



Y 2 



