DENDY— HOMOSCLEROPHORA AND ASTROTETRAXONIDA 233 



surface and strongly hispid in places, especially along part of the margin, where dense 

 tufts of oxea project for as much as 3 mm. ; the entire crust is about 55 mm. in length 

 and 27 mm. in greatest breadth ; irregularly oval in shape. E..N. x. 2 and x. 3 are 

 essentially similar to R.N. x. 1. R.N. vi. (Plate 44, %. 2 a), on the other hand, has the 

 form of a thick, vertical, wall-like plate, attached without any spreading base to a stone. 

 The two sides of the plate are flattened but rather uneven, the margin broadly rounded, 

 the surfaces alike, coarsely granular in appearance but at the same time slightly hispid in 

 places. The entire specimen measures about 50 mm. in length, 30 mm. in height and 

 18 mm. in maximum thickness. R.N. ix. 1 closely resembles R.N. vi. 



None of the specimens show any oscula. The texture is compact, firm and very 

 harsh to the touch. Colour in spirit pale, dull yellow. 



The skeleton is a dense, confused mass of large and small calthrops and small meso- 

 trisenes, penetrated here and there by loose wisps or bundles of oxea, running towards 

 the surface. The relative numbers of the large and small calthrops vary greatly in 

 different specimens. The microrhabds are abundantly scattered all through the sponge 

 but are accumulated in an especially dense layer at the surface. 



Spicules. (1) Large calthrops or short-shafted trisenes (Plate 45, figs. 3 a — 3 a"). 

 Rays generally about equal in length, sometimes straight and sometimes curved or 

 crooked; sometimes sharp-pointed and sometimes rounded off, sometimes (in R.N. ix. 1) 

 reduced to rounded knobs, so that the whole spicule may become almost spherical 

 (fig. 3 a") ; occasionally divided into two short branches at the extremity (figs. 3 a, 3 a') ; 

 size very variable ; rays measured up to about 1"5 by 0'15 mm. 



(2) Small calthrops or short-shafted tricenes (figs. 3 6, 3 6'). Rays usually straight, 

 gradually sharp-pointed ; sometimes differing a good deal in length, while more frequently 

 the three which are alone fully visible at the same time appear to be about equal ; length 

 very variable, say about 0'2 mm., with a diameter of about 0'03 mm. Numerous inter- 

 mediate sizes between these and the large calthrops also occur. 



(3) Mesotrisenes (figs. 3 c — 3 c"). The three cladi spring from about the middle of 

 a short shaft. The cladi are always branched, usually bifurcating once only but occasionally 

 twice. All the cladi and both ends of the shaft are gradually sharp-pointed. Size very 

 variable, say about 0"2 mm. across the cladome, from tip to tip of cladi, in R.N. x. 1, but 

 may be at least twice this size in R.N. vi. Each half (ray) of the straight, unbranched 

 shaft (rhabdome) is about as long as the cladi, An abnormal form with four cladi has 

 been met with and one with only one ray of the rhabdome developed. 



(4) Oxea (fig. 3 d). Very long, straight and slender ; tapering very gradually to 

 each extremity; measured up to 7 '7 by 0'04 mm. 



(5) Amphiasters (fig. 3 e). The shaft between the two whorls of rays is so short 

 that the spicule looks hke an oxyaster, especially when seen obliquely or end on, but 

 I think it is really an amphiaster. The rays are long, slender and sharply pointed, 

 altogether about 10 in number. Total diameter of spicule about 0'016 mm. These 

 spicules are abundantly scattered through the sponge. 



(6) Smooth microrhabds (fig. 3f). Oval, measuring about 0-012 by 0*006 mm. 

 Extremely abundant throughout the sponge, but especially so at the surface. Sometimes 



SECOND SERIES— ZOOLOGY, VOL. XVIL 30 



