GEODIA ATAXASTRA. 



91 



thick-rayed oxyasters (Plate 43, figs. 36, 37a) are connected with the relatively 

 thin-rayed ones (Plate 43, figs. 35, 38) by numerous transitions, which form a 

 continuous series, it does not appear advisable to separate them. 



The large oxyasters of var. latana are on the whole similar to those of 

 var. angustana, but considerably smaller. Diactine oxyasters and asters with 

 branched rays were not observed in this variety. The increase in the size of the 

 spines towards the end of the ray is not so marked in the oxyasters of this 

 variety as in those of var. angustana. The large oxyasters of var. latana have 

 from three to eleven rays, the three- to seven-rayed are 17-28 fi, the eight- to 

 eleven-rayed 15-21.5 p. in total diameter. The basal thickness of the rays is 

 0.7-1.8 ji. 



The oxysphaerasters with slender' spiny rays (Plate 43, figs. 29-32; Plate 44, 

 fig. 29e, 34e) occur in fair numbers in both varieties. Those of var. angustana 

 consist of a spherical centrum 2.6-5.5 jx, that is about a third, of the whole 

 aster, in diameter, from which eighteen to twenty-eight regularly distributed 

 rays arise radially. The rays are straight, conical, and sharp pointed. Their 

 distal parts bear spines of considerable size, some of which are often arranged 

 in a verticil, situated some distance below the tip. The rays are, without 

 the centrum, 3.5-5 p. long and at the base 0.7-1.3 p thick, the total diameter 

 of the aster being 8-13 /<. The spined oxysphaerasters of var. latana have 

 eighteen to twenty-one rays and resemble those of var. angustana very closely 

 but are somewhat larger and have relatively smaller centra. Their dimensions 

 are: centrum 2.4-3.5 /x, a fifth to a third of the whole aster, in diameter; rays, 

 without the centrum, 4-5.5 ^ long and at the base 1.2 thick; total diameter 

 10-14.4 p. 



In both varieties a few asters transitional between the oxyasters and oxy- 

 sphaerasters above described, in regard to ray-number, size, and development of 

 the centrum, have been met with. 



The rare oxysphaerasters with stout smooth rays, which have been observed 

 only in var. latana, have a centrum 4.5 p, that is a little over a third of the 

 whole aster, in diameter, and about eighteen, regularly distributed, straight, 

 smooth, conical, and rather blunt rays, which are, without the centrum, 4.5 p 

 long and at the base 2 p. thick. The total diameter of the aster is about 13 p. 



The small strongylosphoerasters (Plate 43, figs. 33, 34, 37b; Plate 44, figs. 

 30b, 31b, 33-35b, 40b) are exceedingly abundant in both varieties. Those of 

 var. angustana have a more or less regularly spherical centrum, 0.6-2.3 p, ex- 

 ceptionally as much as 3 /i, a sixth to a half of the whole aster, in diameter, 



