78 



GEODIA JAPONICA. 



often they are so small that they can hardly be made out and in some of these 

 asters the rays seem to be quite smooth. The total diameter of the oxysphaer- 

 asters is 17-22 ji. As stated above transitional forms connect these oxy- 

 sphaerasters with the oxyasters. Sollas also mentions these asters. He gives 

 their diameter as 20 ^. Thiele did not find any such asters in the specimens 

 examined by him and expresses the opinion that the ones described by Sollas 

 were young sterrasters. In the type of Sollas I found these asters fairly abun- 

 dant; they have a centrum about b p. m diameter, from sixteen to twenty 

 conical, sharp-pointed rays, at the base 1.4-2 //thick, and measure 15-21 /x in 

 total diameter. 



Most of the small str on gylosphaer asters (Plate 39, figs. 10-12, 13b, 27b, 36, 

 37) are regular, but irregular forms also occur in small numbers. The regular 

 forms have a spherical centrum, 1.2-5 p., usually about one to two thirds of the 

 whole aster, in diameter, from which from twelve to twenty-one equal, con- 

 centric, and regularly arranged radial rays arise. The rays are (without the 

 centrum) 0.6-2 jx long, at the base 0.5-1.2 /i thick, and cylindrical. The end is 

 truncate or rounded. The basal part of the ray is smooth, the end bears spines, 

 which often form a verticil just below the tip. The total diameter of the regu- 

 lar small strongylosphaerasters is 4-6, usually 5-5.5 /i. In the few-rayed forms 

 with 12-13 rays the rays are, as a rule, relatively longer and more slender than 

 in the many-rayed forms with 15-22 rays. 



The irregular small strongylosphaerasters have a centrum 1.5-3.6 //in diame- 

 ter, from which from six to nineteen rays arise. These are irregularly arranged, 

 unequal in length, not always concentric, and usually entirely covered with 

 spines. The rays are (without the centrum) 1.6-3 p long and, at the base, 

 0.6-1.3 n thick. The total diameter of the irregular strongylosphaerasters is 

 5.8-7.3 /(. 



The diameters of the small strongylosphaerasters given by Sollas and Thiele 

 are 5 p and 4 p. respectively. In the type of Sollas reexamined by me these 

 asters have a centrum 1.5-2.2 /t in diameter, from sixteen to twenty rays 

 0.6-0.8 /J. thick, and measure 4-5.5 p. in total diameter. 



The sterrasters (Plate 39, figs. 28-32, 34, 35) are flattened ellipsoids 80-89 p 

 long, 65-78 p broad, and 55-61 p thick. The average proportion of length to 

 breadth to thickness is 100: 83: 58. The freely protruding rays which surround 

 the umbilicus have transverse sections elongated in a direction radial to the 

 centre of the umbilicus, mostly measuring 2.5X4 p, and bear five or six lateral 

 spines. The spines directed towards the umbilicus are larger than the others. 



