134 GEODIA AGASSIZII. 



In one kind of storroid (Plate 31, figs. 3, 4; Plate 32, figs. 33, 34, 36-39; 

 Plate 33, fig. 10) the free distal parts of the rays are considerably thicker, 4- 

 13 /tin transverse diameter, and farther apart than in the normal sterrasters. 

 Some of them, chiefly those surrounding the umbilicus, but also others, have 

 an irregularly elongated transverse section. In these sterrasters the thick rays 

 bear, besides a terminal verticil of from eight to fourteen lateral spines, rather 

 larger than those of the normal sterrasters, several others which arise obliquely 

 from their terminal face. 



In another form of sterroid (Plate 31, figs. 8-10; Plate 33, figs. 9, 14) 

 the freely protruding distal parts of the rays are not very much thicker, 

 but very much farther apart than in the normal sterrasters, and provided with 

 very different spines. The part of the surface of the solid centrum lying between 

 0the protruding rays is in these sterroids covered by large munbers of small 

 projecti(jns of various shape, and appears irregularly granular. Each ray bears 

 from two to eight mostly lateral, but in part also terminal, spines, which are 

 2.5-5 ji long, up to 3 // broad, slightly curved down at the end and covered 

 with numerous small secondary spinelets. When viewed from above, the 

 spines are somewhat similar to serrated leaves. 



In a third kind of sterroid (Plate 32, figs. 25-28; Plate 33, fig. 11) the 

 rays are thicker, up to 15 /i in transverse diameter, and farther apart than in 

 the forms above described. They are terminally rounded and covered with large 

 numbers of recurved, somewhat claw-like spines. In most of these sterrasters 

 the rays are all fairly equally developed, their free distal parts covering the whole 

 of the solid centrum of the spicule and protruding equally far beyond it (Plate 32, 

 figs. 25, 26). In some, however, there are only a few groups of protniding rays, 

 the greater part of the surface of the centrum being destitute of such (Plate 32, 

 figs. 27, 28) but covered with groups of spines similar to the spines on the pro- 

 truding rays. 



In the specimens from Station 4228, both the young and the adult, I have 

 found a few oxysphaerasters, about as large as the sterrasters, three in the 

 former and one in the latter. These spicules have from thirteen to fifteen 

 straight, conical and smooth, radial and concentric, rather irregularly distributed 

 rays. They measure 90-100 /« in total diameter; the diameter of the centiiim is 

 25-27 /«; the rays are (without the centrum) 35-40 fi long and 10-17 /« thick at 

 the base. I found these asters in situ in sections in the subcortical layer and 

 I do not think that they are foreign to the sponge. For the reasons given 

 below, I considered them as sterroid-derivates. 



