HYALONEMA (OONEMA) HENSHAWI. 329 



ax-e siniilai- to those of the gastrals and 42-70 ,u long. The proximal ray of 

 the single hexactine form observed is 30 /u long. 



The canalar pijiules (Plate 97, fig. 6) are pentactine or, more rarely, hexac- 

 tine. The distal ray is 120-220 ^ long and 6-10 m thick at the base. The 

 lateral rays are 53-110 n long; the proximal ray is, when present, 28-65 ^ long. 

 All the rays are pointed, conical, and spined. The spines are very small, so that, 

 even with the spines, the distal ray is nowhere thicker than at its base. 



The hypodermal and hypogastral penlactines. A large number of hypodermal 

 pentactines were obser\'ed, but few hypogastral. The hypogastrals and hypo- 

 dermals appear to be quite similar. Their rays are straight, smooth, conical, 

 and blunt. The proximal ray is 550-900 fi long and 26-47 ^ thick at the base. 

 The lateral rays are 320-650 /x long. 



The hexactine megascleres are 0.6-1.4 mm. in diameter, and have fairly 

 straight, conical, and blunt rays, 13-32 n thick at the base. 



The amphioxes are centrotyle, nearly straight or curved, rarely angularly 

 bent near one end. They are 0.9-1.6 mm. long and 8-23 m thick near the 

 middle. The central tyle is 12-27 n in transverse diameter, that is 1-6 ^ more 

 than the adjacent parts of the spicule. 



The rays of the microhexactines (Plate 97, figs. 33-36) are nearly always 

 perfectly straight; only quite exceptionally one of the rays exhibits a slight 

 curvature. The microhexactines are 108-230 ^ in diameter, generally 110 

 190 IX, and their conical, pointed rays are 3.5-7 n thick at the base. The rays 

 bear spines, the largest of which are 0.7-1.5 n long. Generally the spines are 

 sparsely scattered over the greater part of the length of the ray, leaving the 

 distal end-part free for a distance of about 10 m- The proximal spines are 

 vertical, the distal inclined backwards. 



Among the amphidiscs two kinds can be clearly distinguished morphologi- 

 cally: — A, a. stout kind with large anchors, about half the length of the whole 

 spicule; and B, a slender kind with small anchors, much less than half, usually 

 about a third, of the whole spicule in length. 



The length frequency-cm'\'e (Figure 20) has three main elevations sepa- 

 rated by deep depressions. The part of the curve to the right of 106.72, the 

 summit of which Ues at about 179, pertains to the morphological group A, 

 and comprises all amphidiscs of this kind. The deep depression (down to 0) 

 between this part of the curve and the other parts shows that the amphidiscs 

 it pertains to form a distinct group. This coincides with their morphological 

 character, and so a special group must doubtlessly be established for these 



