GEODIA VARIOSPICULOSA. 



65 



The number of rays is, as shown by the following table, roughly speaking, 

 in inverse proportion to their size. 



NUMBER AND SIZE OF RAYS OF OXYASTERS. 



Oxyasters with from nine to eleven rays are very rare. The largest of them 

 observed was 23 // in total diameter and had rays \2 n long and 2 // thick at the 

 base. 



The oxysphaerasters (Plate 18, fig. 23; Plate 19, figs. 12a, 13a) are composed 

 of a spherical centrum and numerous regularly distributed, concentric, radial 

 rays. The rays are in the same aster of equal size, conical, sharp pointed, and 

 sparsely spined. Often a verticil of larger spines, situated some distance below 

 the end of the ray is observed. The oxysphaerasters of var. micraster usually 

 have from eighteen to twenty-two rays. Their total diameter is 14-19 /i, the 

 diameter of the centrum 5-6 //. The rays are 4-7 p. long and 1-2 fi thick at the 

 base. The oxysphaerasters of var. intermedia usually have from fourteen to 

 twenty-two rays. Their total diameter is 17-22 fi, the diameter of the cen- 

 trum 5-6 fi. The rays are 5-8 fi long and 1.5-2 fi thick at the base. A cor- 

 relation between ray-number and spicule-size is not apparent. 



The small dermal strongylosphaerasters (Plate 19, figs. 12b, 13b, 19-24) 

 consist of a spherical or irregularly tuberous centmm and numerous short rays. 

 The rays are usually stout, cylindroconical, or cylindrical, and truncate, rarely 

 more slender, conical, and blunt pointed. Not infrequently the rays of the same 

 aster are unequally distributed and unequal in size, one of the rays being some- 

 times fully twice as large as any of the others. The distal parts of the rays, 

 chiefly their terminal faces, bear numerous small spines. In var. mici'aster the 

 strongylosphaerasters usually have from ten to eighteen rays. Their total 

 diameter is 5-8 /z, the diameter of the centrum 2-4 /i. The rays are 0.5-2.5 fi 



