352 
HYALONEMA (OONEMA) SEQUOIA. 
The small and stout amphioxes (Plate 89 , fig. 15b) are centrotyle, fairly 
straight, 0.6-2. 5 mm. long, and 22-70 n thick near the middle. The proportion 
of length to thickness is in these spicules 1000 : 17 to 1000 : 31. The central 
tyle is 24-75 /x thick, that is 1-7 /x more than the adjacent parts of the spicule. 
The large amphioxes ( tignules ) (Plate 89 , figs. 1-5) are slightly and irregularly 
curved, not centrotyle, and not exactly cylindrical in the middle or uniformly 
thickened toward it; the outline is slightly wavy. They are 5-8 mm. long and 
100-140 ijl thick. The proportion of length to thickness is in these spicules 
1000 : 15 to 1000 : 20. 
The acanthophores (Plate 85 , figs. 9-19) have one to six, most frequently 
four rays. The diactines are centrotyle. The forms with 
5-6 rays are 140-224 m in maximum diameter and have rays 10-28 n thick, 
3-4 “ “ 95-435 “ “ “ “ “ 
2 “ “ 212-1050 “ long and near the central tyle 
1 ray is 108-180 “ “ “ “ “ terminal tyle 
“ 15-36“ 
14-18 “ 
20-30 “ 
U 
U 
u 
The central tyle of the long diactines is usually 5-7 yu more in transverse 
diameter than the adjacent parts of the spicule. In the smaller tetractines the 
four rays are usually fairly equal; in the larger one ray, or two opposite rays, 
are often longer than the others. All the long-rayed (diactine) forms and a 
few of the short-rayed (mon- to hexactine) ones have rays smooth in their proxi- 
mal and middle-parts and spined only in their end-parts. Most of the mon- 
to hexactine forms are spined throughout, the terminal spines being, as a rule, 
considerably larger than the more proximal ones. The spines are vertical, 
broad, low, conical, and pointed. 
The stalk-spicules are all broken off at the distal end. The parts present 
have a maximum thickness of 0.2- 1.2 mm. 
The microhex actines (Plate 86, figs. 9, 11, 12, 35, 36; Plate 88, figs. 1-4) 
are 60-200 \x in diameter, generally 95-170 /x, and have equal, regularly arranged 
rays. The rays are perfectly straight, 4-6 /j. thick at the base, conical, and sharp- 
pointed. Everywhere except at the extreme tip they bear spines. The spines 
on their proximal half arise vertically; beyond that they incline more and more 
backward, towards the centrum of the spicule. The largest spines are those 
arising at a distance of about a third of the length of the ray from the centrum. 
Here they are about 1.5 jx long, and from here they decrease in size, both distally 
and proximally. 
