GEODINELLA ROBUSTA. 215 



are particularly large, and very regularly arranged in verticils. These large 

 spines arise vertically from the ray and often appear to be bent down at the 

 end so that they become claw shaped. Also in the oxyasters and oxysphaer- 

 asters of this variety an inverse relation between the number of rays and the 

 size of the spicule is discernible; the asters under 20 n in diameter having from 

 nine to seventeen, the asters over 20 n in diameter, from six to eleven rays. 

 The oxyasters and oxysphaerasters of var. megaclada are smaller than those of 

 var. megasterra, only 11-30 jj. in diameter, and have on an average more rays, 

 the small ones (under 20 ft in diameter) up to twenty, the large ones (over 20 fi 

 in diameter) eleven to fifteen. 



The strongylosphaerasters (Plate 2, figs. 3b, 8, 9, 10c; Plate 4, figs. 18-20) of 

 var. carolae consist of a spherical, central thickening, from which from eleven 

 to twenty-seven radial rays arise. The whole aster is 7-12 /i in diameter. The 

 diameter of the central thickening is usually from one half to two thirds of the 

 diameter of the whole spicule and measures 3.5-7 /i. The rays are cylindrical 

 and arise from the central thickening with trumpet-shaped basal extensions. 

 They are 2-3 n long, 1-1.7 n thick, and terminally rounded. The distal parts 

 of the rays are covered with small spines which often form a conspicuous terminal 

 verticil (Plate 4, fig. 19). A correlation between the size of the spicule and the 

 number of rays is not discernible. In var. megaclada the maximum dimensions 

 of these spicules are similar, but the minimum dimensions greater. The 

 strongylosphaeraster of this variety measured were 10-12 a in diameter, and 

 had from nineteen to twenty-five rays and a central thickening 5-7 jx in 

 diameter. Among the strongylosphaerasters of this variety I have observed 

 many in which the verticillate arrangement of the ray-spines was particu- 

 larly well marked, and I noticed that in many of these the spines of the verticils 

 are recurved. The rays of these spicules, particularly when viewed from above, 

 closely resemble sterraster-rays. In var. megasterra the strongylosphaerasters 

 are also similar, but here they attain a somewhat larger size, measure 8-13 /< in 

 diameter, and have fewer, only from twelve to nineteen, rays; the central thick- 

 ening is 3.5-7 n in diameter. 



Sometimes sphaerasters, similar to these strongylosphaerasters, but with 

 rays distinctly tapering towards the distal end, are observed. These spicules 

 are transitional to the small oxysphaerasters. I have noticed such si)liaeras- 

 ters particularly in var. carolae. 



The normal sterrasters (Plate 2, figs. 1, 2, 5; Plate 3, figs. 1-3, 7, 9; Plate 4, 

 fig. 13). As stated above the size and shape of the normal sterrasters are 



