130 



GEODIA A(;ASSIZII. 



three times as great as the basal tliickness of tlie rays. The rays are usually 

 radial and quite regularly distributed only in the rare, exceptionally large, 

 few-rayed oxyastei-s of the adult specimen from Station 4228 is an irregular dis- 

 tribution of the rays observed. The rays are straight, at the base 0.8-3.2 /< 

 thick and conical. They taper uniformly to the end, which is pointed, blunt, 

 roundc-d, or rarely, truncate. The distal parts of the rays are always more or 

 less spiny. In some oxyasters the spines extend down nearly to the base of the 

 rays, in others they are confined to the distal two thirds, and in a few — such as 

 I have found chiefly in the si:)ecimens from Station 4199 — they are more or less 

 restricted to verticils lying just below the tips of the rays. The oxyasters with 

 spines arranged in this manner appear somewhat acanthtylaster-like. The 

 oxy;xsters of the adult specimens measure 9-31 [i in diameter, their average 

 maximum diameter being 24.22 [i. Oxyasters more than 26 n in diameter with 

 irregularly distributed rays have been met with only in the adult specimen from 

 Station 4228. Among the others the specimens from Stations 3168 and 4551 

 have the largest, those from Station 4199 the smallest oxyasters. The size of 

 these asters is in inverse jDi'oportion to the number of their rays. None of the 

 oxyasters over 20 /< in diameter observed by me had more than nine rays, 

 all those with ten or more rays being less than 20 n in diameter. The large 

 choanosomal oxyasters of the young specimen from Station 4228 are similar to 

 those described above, usually have from nine to fourteen rays 0.8-1.7 ji thick 

 at the base, and measure 13-25 fx in total diameter. In the immature speci- 

 men described by Lambe the oxyasters have from seven to nine rays 1.3-2.3 n 

 thick and a central thickening; their total diameter is 13-20 /«. 



TOTAL DIAMETERS OF THE LARGE OXYASTERS OF GEODIA AGASSIZII. 



The large oxysphaerasters (Plate 26, fig. 14; Plate 27, figs. 4c, 14c; Plate 

 30, fig. 3) appear to be more numerous in the specimens from Stations 2886 

 and 3168 than in those from the other stations. The oxysphaerasters of the 

 adult specimens consist of a spherical central thickening (centrum), 3.5-11 /i in 

 diameter, from which from fourteen to twenty-eight and perhaps more (it is 

 exceedingly difficult to count them accurately) equidistant radial rays arise. 

 These are usually shorter than the diameter of the centrum, regularly conical. 



