Dr. G. J. Ilinde on the Oenus Hindia. 77 



extending from a common inflated centre. Three of the rays 

 are either straight or slightly curved, subequal, cylindrical in 

 section and with expanded extremities ; they form by their 

 union, as Duncan has already stated, a tripod-shaped body 

 from the upper surface of which the fourtli ray projects. 

 This fourth ray is always considerably shorter than the others, 

 and in most cases is merely a short stumpy process, terminating 

 in from two to four small, conical, slightly divergent spurs. 

 In the silicified specimens (fig. ] , b-e) the frilled convex bor- 

 ders and extremities of the tripodal rays are considerably 

 eroded, and the spurs of the fourth ray are only faintly indi- 

 cated {b, 4) ; but they can be distinguished in the connected 

 meshwork slightly projecting into tlie interspaces, even when 

 the ray itself is concealed (fig. 1, «). The inflated nodes or 

 centres of the spicules cannot be made out in a longitudinal 

 section of the sponge (flg. 1, a), and even in a tangential 

 section, owing to the manner in which the rays overlap each 

 other, this character is masked (fig. 2) ; but in the detached 

 spicules the centres are clearly shown (fig. 1, d^ e). 



The connected structure of the skeleton can be readily 

 understood when once the true form of the individual spicules 

 has been ascertained. In all cases the fourth or truncated 

 ray points to the exterior of the sponge. The three diverging 

 tripodal rays of each spicule extend towards tlie central nodes 

 of three different proximate spicules next below, and their 

 expanded terminations are intimately apposed to the centres 

 and convex borders of the rays of these spicules. But as 

 each spicule is connected by three rays with three diflferent 

 spicules of the proximate series below, so also does each sup- 

 port, on the upper portion of its node, three rays of difterent 

 spicules which converge to it from the series above. The 

 ends of these three converging rays are thus grouped round the 

 truncated fourth ray of the spicule in such a manner that, when 

 viewed in a longitudinal section, it is almost entirely hidden 

 by them, and only its summit-spurs can be seen (fig. 1, a). 

 The fourth ray thus serves as a centre and support for the 

 rays converging to the spicule from above, and thus materially 

 contributes to the firmness and strength of the skeleton. 



Owing to the inflation of the central nodes of tlie spicules, 

 the canals radiating from the central space to the surface of 

 the sponge are subcircular or subelliptical in transverse section 

 (fig. 2), the spicular nodes occupying the position of the angles 

 shown in Dr. Raufi:''s diagrammatical figure *. The indi- 

 vidual spicules and their union can hardly be distinguished 

 in the tangential section (fig. 2), although drawn on the same 

 * ' Auuals/ Sept. no., fig. 2, p. 174. 



