184 
HYALONEMA (HYALONEMA) AGASSIZI. 
sponge-body, particularly in form C, apparently connecting these slender-rayed 
acanthophores with the modified basal pinules described above on the one hand, 
and the stout acanthophores described below, on the other hand. 
The stout acanthophores surrounding the proximal end-parts of the large 
stalk-spicules (Plate 45 , figs. 1-4, 14-17, 24, 25, 35-39) are mostly tetractines 
and diactine tetractine-derivates. However, similar pentactines, triactines, and, 
exceptionally, also monactines occur among them. Occasionally one meets 
with tetractines and pentactines of this kind with all the rays greatly reduced 
in length. These spicules appear as transitions, leading to the spheres described 
below. 
The rays of the same spicule are always more or less, and sometimes very 
unequal. They generally join at angles of about 90° or 180°, and are straight 
or curved, and cylindrical and terminally rounded, or conic and either blunt or 
pointed at the end. The diactine ones are either centrotyle or simply cylindrical 
in the centre, straight, slightly angularly bent in the middle, or, rarely, strongly 
curved. One 11 m thick, which I observed in form A, formed a complete ring 
65 m in diameter. Sometimes the rays bear rudiments of branch-rays. The 
basal parts of the rays are usually smooth or only sparsely spined ; their end-parts 
bear numerous, rather large, generally nearly vertical spines, which stand close 
together. The smooth proximal part is usually a little longer than the spined 
distal part. 
In form A the larger, normal acanthophores are 200-690 m in maximum 
diameter and have rays 14-40 n thick at the base. The small ones transitional 
to the spheres (Plate 45 , figs. 24, 25, 38) are 46-115 in diameter and have rays 
9-14 /x thick. 
In the other forms these spicules appear to be similar. Form D possesses 
mon- to pentactine spicules of this kind 195-550 ^ in maximum diameter with 
rays 15-35 /x thick. The monactines are very rare. One that I measured was 
195 n long, and at the rounded, somewhat thickened end, 12 ^ in transverse 
diameter. 
In the preparations of one of the specimens of form F the stout acanthophores 
are particularly numerous. The triactine and tetract.ine forms here measure 
120-640 /x in diameter, usually 420-590 /x, and have rays 20-40 m thick at the 
base. The diactine forms are usually fairly straight, rarely strongly angularly 
bent in the middle so that the two rays enclose an angle of 90° or less. The 
fairly straight diactines are 120-550 m long. Their rays have the same thickness 
as those of the triactines and tetractines. 
