184 HYALONEMA (HYALONEMA) AGASSIZI. 



sponge-body, particularly in form C, apparently connecting these slender-rayed 

 acantliophores 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 cUactine 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 ix in maximum 

 diameter and have rays 14-40 ^ 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 M thick. 



In the other forms these spicules appear to be similar. Form D possesses 

 mon- to pentactine spicules of this kind 195-550 n in maximum diameter with 

 rays 15-35 /x thick. The monactines are very rare. One that I measured was 

 195 M long, and at the rounded, somewhat thickened end, 12 m in transverse 

 diameter. 



In the preparations of one of the specimens of form F the stout acanthophores 

 are particularly numerous. The triactine and tetractine forms here measure 

 120-640 M in diameter, usually 420-590 m, and have rays 20-40 fi 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 fj. long. Their rays have the same thickness 

 as those of the triactines and tetractines. 



