274 ART. 7. 1. IJIMA : HEXACTINELLIDA, IV. 



the same spicule, shows no swelling in its course but gradually 

 tapers like the rest of the rays, whereas in II. mirabilis the 

 same ray should be thickened in the middle. The microtubercles 

 on that ray are more numerous and somewhat more strongly 

 developed than on all the other rays on which tliey appear 

 rather sparsely. 



The oxyltexaslers, which occur abundantly in all parts, 

 measure 130-100/^ in diameter. Those situated in the periphery 

 of the wall are mostl}" normal, having usually two and occasionally 

 three, slender (about 2 /^ thick at base) and obsoletely rough 

 terminals to a principal, the latter being very short (PI. XXI., 

 figs. 4 and 5). It seems that the terminals are very easily broken 

 off at base, for it is seldom that one meets with an oxyhexaster 

 of this variety in a perfectly intact state. 



In the deeper parts of the wall the oxyhexasters change in 

 their character, though in general size there exists no appreciable 

 difference (PL XXL, figs. 6-8). Thus, in the subgastral region 

 as well as in the endosome they are scarcely ever normal but 

 are nearly always hemihexactinose and occasionally regularly 

 hexactinose. Moreover, the terminals are quite smooth throughout 

 and are considerably stronger than in the peripheral oxyhexasters. 

 — sometimes fully twice as thick at base as in the latter. The 

 exceedingly short principals bear at the most two terminals. 



The discodasters (PI. XXL, figs. 10 and 11) resemble in 

 shape and size those of E. mollis or R. mirabilis. They are 

 found more abundantly in, as well as directly under, the ectosome, 

 than in the deeper parts. Diameter, 175-190 /-«. The six bosses 

 on the central node are sometimes distinct and sometimes not. 



