GEODIA JAPONICA. 



77 



enclose angles of 30-54°, on an average 39°, with the axis of the rhabdomc. 

 Such spicules are not mentioned either by Sollas or by Thiele neither could I 

 on examination find any in the type of Sollas. 



The large oxyasters (Plate 39, figs. 13a, 18-26, 27a) usually have no central 

 thickening, and from three to seven equal, concentric, regularly distributed 

 rays. The rays are straight, conic, blunt, and everywhere, except quite at the 

 base, thickly covered with spines. The spines appear to increase in size towards 

 the end of the ray; those large enough to be clearly made out, are somewhat 

 recurved, claw shaped. The size of the whole aster antl of the rays is in 

 inverse proportion to the number of the latter. 



NUMBER OF RAYS AND DIMENSIONS OF OXYASTERS. 



Number of rays 



Total diameter of asters 



Length of rays 



Thickness of rays at base 



3-4 



30-46 n 



18-23.5 fi 



2-2.8 !i 



5-6 



27-39 /( 



15-21 /( 



1.2-2.7 /( 



7 



25-31 /i 



13-16 n 



1.3-1.8 /( 



Occasionally small oxyasters with a distinct centrum and more than seven 

 rays are observed. These may be considered as transitional between the true 

 large oxyasters described above and the large oxysphaerasters described below. 

 According to Sollas the large oxyasters are 32 ft in diameter. He describes their 

 rays as smooth. Thiele says that the rays of the oxyasters are few in number 

 and 6-14 ft long. In the type of Sollas I found that the large oxyasters have 

 from three to seven straight, spined rays. The rays are usually conical and 

 pointed; very rarely some of them are reduced in length and terminally rounded. 

 The rays are, at the base, 1.8-2.8 /i thick. The total diameter of the aster is 

 21-36 11. 



The large oxysphaerasters (Plate 39, figs. 27c, to the right, 33, 40, 41) have 

 a spherical centrum, 5-7.5 /«, usually not quite a third of the whole aster, in 

 diameter, from which from fifteen to twenty-one concentric, regularly arranged 

 radial rays arise. Usually the rays are equal, rarely one or more reduced in 

 length and rounded at the end. The normal rays are conical, sharp pointed, 

 (without the centrum) 5.5-8 /i long, and, at the base, 1.9-2.5 ft thick. They 

 bear a small number of spines, which are usually restricted to a belt lying 

 some distance below the end. Sometimes the spines are rather large and then 

 one perceives that they are slender and directed obliquely outward. More 



