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 55, 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 u long, and about 
5 » 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». The 
lateral rays are pointed, spiny, and usually 28-45 u long. 
The pentactine megascleres (Plate 55, figs, 2, 3) have straight, conic rays, 
20-40 » 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 u 
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 mm. 
long and 4-20 » 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 microhexactines (Plate 55, figs. 34, 37) measure 85-184 » in diameter, 
most frequently about 1504, and have six equal, perfectly straight, conic, 
sharp-pointed rays, usually 2-3 » thick at the base. The rays bear oblique, 
outwardly directed spines. These are numerous and very small, usually under 
0.5 w in length. 
Of amphidiscs three kinds are to be distinguished: — macramphidiscs, large 
micramphidiscs, and small micramphidises. 
The macramphidiscs (Plate 55, figs. 5, 14-18) are 285-349 u long, most fre- 
quently about 315 4. The shaft is straight and near the centre, where it is 
thinnest, 6-9 » in transverse diameter. It is generally thickened abruptly in 
the middle to a central tyle 10-13 » in diameter. Toward the ends it is always 
