GEODTA AGASSIZII. 



131 



1-2 ji thick at the base, and sharp or blunt pointed. From the distal parts of 

 the rays a few quite large spines arise. These are often arranged in a some- 

 what verticillate manner near the tip of the ray. These oxysphaerasters are 

 10-21 ju in total diameter, the average maximum being 18.2 /«. In the young 

 specimen from Station 4228 the large oxysphaerasters have from eighteen to 

 perhaps thirty rays and measure 12.5-18 a in total diameter, the diameter of 

 the centrum being rather less than in the oxysphaerasters of the adult specimens 

 and rarely exceeding 4 /i. In the immature specimen described by Lambe 

 the oxysphaerasters have from ten to twenty rays, 0.9-2 /£ thick, the centre is 

 2.7-7 p., the whole aster 8-21 ^, in diameter. 



TOTAL DIAMETER AKD DIAMETER OF THE CENTRUM OF THE LARGE OXYSPHAER- 

 ASTERS OF GEODIA AGASSIZII. 



The small strongylosphaerasters (Plate 26, fig. 15; Plate 27, figs. 3-14d; 

 Plate 30, figs, la, 2a, 6-9, 10a; Plate 32, figs. 2, 3) are abundant in all specimens. 

 They consist of a central sphere (centrum), from which from six to twenty 

 fairly equidistant rays arise radially. The length of these rays is usually smaller, 

 rarely as great as or greater, than the diameter of the centrum. In the small 

 strongylosphaerasters of the adult specimens the rays are at the base 0.6-1.6 /< 

 thick and taper towards the truncate end, or are nearly cylindrical (Plate 30, 

 figs. 6-9). The rays bear small spines, which often appear massed at their ends. 

 The total diameter of these asters is 3.5-11 fi, the average maximum being 9.1 fi. 

 The centra are 1.5-6 pi in diameter, the average maximum being 4.3 /«. The 

 centra of the small strongylosphaerasters of the specimens from Stations 2978 

 and 4193 are smaller than the centra of those of the others. The small strongy- 

 losphaerasters of the young specimen from Station 4228 are similar to those 

 of the adult specimens. They usually have from twelve to nineteen rays 

 0.5-1 /i thick; and a centrum 2-3 /i in diameter; their total diameter is 5.5- 

 9 /i. In the immature specimen described by Lambe the small strongylo- 

 sphaerasters have from ten to twenty-eight rays 0.6-1 /« thick, the centre is 

 2-3.5, the whole aster 5-7 /i, in diameter. 



