HYALONEMA (OONEMA) CRASSIPINULUM. 339 



and third kinds, because in other closely allied species they are not so clearly 

 separated biometrically. I distinguish accordingly two main groups of amphi- 

 discs: — macramphidiscs 110-480 ix long, and micramphidiscs 31-10() /x long. 



The macramphidiscs comprise the first, second, and third kinds of amphi- 

 discs. As shown above, the first kind is veiy clearly distinguished from the 

 second and third both morphologically and biometrically. I therefore divide 

 the macramphidiscs into two groups, large macramphidiscs 375-480 /i long, and 

 small macramphidiscs 110-200 m- 



The length frequency-curve of the large macramphidiscs has two distinct 

 elevations. However, in view of the morphological similarity of the largest 

 and the smallest, and the smallness of the number of large macramphidiscs 

 observed and measured, I do not attach much importance to this, and consider 

 the large macramphidiscs as a simple group. 



The length frequency-curve of the small macramphidiscs has a single 

 elevation, and is remarkably regular biometrically. These spicules accord- 

 ingly form a remarkably homogeneous group. Morphologically, however, two 

 kinds of small macramphidiscs are to be distinguished : — those with relatively 

 smaller, chiefly narrower anchors; and those with relatively larger, chiefly 

 broader anchors. 



The micramphidiscs form morphologically a nearly continuous series, the 

 smallest being connected by intermediate forms with the largest with hardly 

 any break. Their length frequency-curve, however, shows four elevations 

 and three depressions, one of which (at about 47.5 n) is rather conspicuous. 

 In view of the sUghtness of the morphological differences between the micram- 

 phidiscs to which the four elevations of the curve pertain, I abstain from sub- 

 di\'iding them into subgroups corresponding to these elevations. 



Thus I distinguish four kinds of amphidiscs in this sponge : — large macram- 

 phidiscs, small broad-anchored macramphidiscs, small narrow-anchored macram- 

 phidiscs, and micramphidiscs. 



The large macramphidiscs (Plate 93, fig. 10) are ^^ery rare. In fact I found 

 only seven in all, and although some of these were observed in the sections, it 

 is not impossible that they are foreign; the probability is, however, greatly 

 in favor of their being proper to the sponge. These spicules are 375-480 n 

 long, most frequently about 468 /x. The shaft is cylindrical, 22-29 ^ thick, 

 smooth, and slightly thickened in or near the centre. The terminal anchors are 

 168-215 n long, about a third of the whole spicule, and 210-260 m broad. The 

 proportion of their length to their breadth is 110 to 107-155, on an average 100 : 



