IGO GKODIA BREVIANA. 



2.3 [1 tliick, and are 19-25 /( (Lambe, 1893, 3-13, according to his figures 

 1 1 -15 /«) in total diameter. 



The rare thin-rayed oxyasters which, as above stated, may be foreign, have 

 from nine to fourteen rays and no centrum. The rays are 3-11 /( long, and very 

 thin, only 0.25-0.7 ft thick at the base. They are not very much attenuated 

 towards the end and bear spines which sometimes form terminal verticillate 

 dustei-s, in which case these astei-s appear as acanthtj-lasters. The total diame- 

 ter of these astei-s is 7-23 /x. If they are not foreign, they may be young forms 

 of the thick-rayed oxyasters described above. 



The lai-ge oxysphaerasters (Plate 35, figs. 21c, 25, 26) have a spherical cen- 

 trum, 7-9 /( in diameter, from which from twent,y-three to twenty-seven straight, 

 conical, and sharp-jwinted, usually regularly distributed rays arise radially. 

 _ These rays are (without the centrum) G-8 fL long and 1 -2.7 // thick at the base. 

 They are covered with a greater or smaller number of good-sized spines. The 

 rays of the oxysphaerasters with twenty-six or twenty-seven raj^s are basally 

 onl}- 1-2.2 n, those of the oxysphaerasters with twenty-three or twenty-four rays 

 basally 2.5-2.7 fx thick. This indicates that there is an inverse proportion 

 between the ray-number and the ray-thickness. The whole aster is 14-21.5 ^ 

 in diameter. In the specimen described by Lambe these asters have up to' 

 thirty rays 1-1.7 fi thick, the centre is 3-5.5 /«, the whole aster 12-18 fi, in diame- 

 ter. They are not mentioned by Lambe (1893). 



The small strongylosphaerasters (Plate 35, figs. 8-13, 18-22b) have a centrum 

 3-5.5 jiL in diameter and usually from thirteen to twenty-one, very rarely only 

 seven or three rays. The rays are generally radial and regularly distributed, 

 rarely arranged irregularly. Such an irregularity is chief!}' observed in the 

 rare few-rayed forms which are evidently derivates of the ordinary many-raj^ed 

 ones, produced by the suppression of a smaller or greater number of rays. The 

 rays are cylindrical or cylindroconical and truncate or terminally rounded. Their 

 ba.sal parts are smooth, their distal parts covered with a number of good-sized 

 spines. The rays are 1.8-5 /z long and 0.6-1.7 /( thick; the whole aster measures 

 7-12 fi in diameter. A correlation between ray-number and spicule-size is not 

 pronounced. In the specimen described by Lambe these asters have from four- 

 teen to twenty-five rays, 0.5-1.2 ^ thick, the centre is 2-4 //, the whole aster 

 6-9 n, in diameter. They are not mentioned by Lambe (1893). 



The sterrasters (Plate 35, fig. 23) are flattened ellipsoids, 87-105 ft long, 

 80-98 fx broad, and 70-77 fj. thick. The proportion of length to breadth to thick- 

 ness is on an average 100 : 91 : 74. In the specimen described by Lambe the 



