360 HYALONEMA (PHIALONEMA) BREVANCORA. 



serrated appearance (Plate 55, figs. 32, 33). The proximal ray, when present, 

 is similar to the laterals, and attains a length of 27 ^ (Plate 65, fig. 30). 



The (probably canalar) pinules with short-spined distal ray (Plate 55, fig. 29) 

 observed by me were all pentactines. The distal ray is 66-85 m long, and about 

 5 M thick at the base. Its spines are straight, conic, small, and directed obliquely 

 upwards towards the tip of the ray. They are largest in the middle of the ray 

 and decrease in size both distally and proximally. The distal end-part of the 

 ray is often, for a considerable distance, quite free from spines. The maximum 

 diameter of the distal ray, together with the spines, is usually about 14 /x. The 

 lateral rays are pointed, spiny, and usually 28-45 yu long. 



The pentadine megascleres (Plate 55, figs. 2, 3) have straight, conic rays, 

 20-40 fx thick at the base, and rounded at the end. The proximal ray is usu- 

 ally 0.8-1.1 mm. long; the laterals are 0.25-0.6 mm. long, and slightly inclined 

 towards the proximal, with which they enclose angles of 78°-84°. 



The hexactine megascleres (Plate 55, fig. 31) observed measured 0.4-0.9 mm. 

 in diameter, and had somewhat unequal, straight, conic, and blunt rays 7-16 n 

 thick at the base. 



The rhabd megascleres (Plate 55, figs. 4, 6) observed are for the most part 

 more or less curved centrotyle amphioxes. These spicules are 0.4-4.5 nmi. 

 long and 4-20 m thick near the centre. The proportion of the thickness of the 

 spicule to the diameter of the tyle is 100 : 125 to 100 : 225, most frequently 

 about 100 : 150. There are besides these spicules centrotyle amphioxes angu- 

 larly bent in the middle (Plate 55, fig. 4) and centrotyle rhabds with one of the 

 actines reduced in length and thickened at the end to a terminal tyle. In some 

 of the latter a kind of terminal spine arises, from the thickened end (Plate 55, 

 fig. 6). 



The ynicrohexactincs (Plate 55, figs. 34, 37) measure 85-184 yu in diameter, 

 most frequently about 150 ii, and have six equal, perfectly straight, conic, 

 sharp-pointed rays, usually 2-3 yu thick at the base. The rays bear oblique, 

 outwardly directed spines. These are numerous and very small, usually under 

 0.5 M in length. 



Of amphidiscs three kinds are to be distinguished: — macramphidiscs, large 

 micramphidiscs, and small micramphidiscs. 



The macramphidiscs (Plate 55, figs. 5, 14-18) are 285-349 ^ long, most fre- 

 quently about 315 n. The shaft is straight and near the centre, where it is 

 thinnest, 6-9 n in transverse diameter. It is generally thickened abruptly in 

 the middle to a central tyle 10-13 n in diameter. Toward the ends it is always 



