STAUROCALYPTUS HETERACTINUS. 221 



The oxyhexasters (PI. XI., figs. 7 and 8) liave a diameter of 

 106-114 It-. They seem to be never hemihexactinose or hexactin- 

 ose. As regards appearance they may be divided into two cate- 

 gories, which seem however to intergradate. '1 he one category 

 (fig. 7) is composed of those mostly lying in the periphery of 

 the sponge-wall, and in them each principal of a perceptible 

 length bears 2-4 (usually 3), slender and obsoletely rough or 

 nearly smooth terminals. To the other category (fig. 8) belong 

 the great majority of the oxyhexasters abundantly present near 

 the "-astral snrface and occasionally a few of those fonnd in the 

 periphery. In these the principals are extremely short and bear 

 each 2 (sometimes 3), strong and distinctly rough terminals. The 

 roughness may be developed into retroverted microspines or barbs 

 on the basal parts of the terminals. 



The discodasters (PI. XL, fig. 6) vary in diameter from 110 

 />« to 200 lu They are tolerably common, especially near the gastral 

 surface. Those in the peripheiy of the wall are on the whole 

 smaller than others more deeply situated. In the former (of 

 which PI. XL, fig. 15, in reality taken from an undetermined 

 Staurocalyiyius, might well pass for a representative) the secondary 

 principals are as slender as 4 /^ or less. In the latter (fig. 6) 

 the same may be fully 6 y thick. Generally speaking, the central 

 node is either plain or is supplied with the six boss-like promi- 

 nences. The secondary principals make up about two-fifths of 

 the entire ray-length. The terminals, 2-7 in number to a prin- 

 cipal, are straight and form a tuft which expands generally but 

 little outwards. The terminal discs appear simply like piidieads. 



The microdiscohexasters (PI. XL, fig. 9) are of the usual 



