304 



ERYLUS ROTUNDUS. 



It has been stated above, that oxyaster-hke spicules similar in size and 

 ray-number to the acanthtylasters, which I consider a young form of the latter, 

 also occur in these sponges. These spicules are rather numerous in var. mega- 

 rhahda, form A, and met with in smaller numbers in var. megarhahda, form B, 

 and in the forms A and C of var. typica. The distal parts of the rays of these 

 asters are exceedingly slender. Proximally the rays thicken considerably and 

 abruptly, so that their basal part appears bulbous. Besides these spicules, 

 which I consider as the earliest known stages, others similar to them, but with 

 thicker and distally rough rays, representing a later developmental stage, are 

 observed. Finally various asters of this kind occur, in which a more or less 

 ])ronounccd spiny thickening crowns the end of each ray. These asters connect 

 the slender-rayed oxyasters with the true acanthtylasters. 



The small many-rayed oxyasters (Plate 6, fig. 14c; Plate 7, figs. 52c, 60c, 76c) 

 are without centrum or have a slight central thickening, in var. typica, form A, 

 up to 4 /( in diameter. There are from eight to twenty-two, or more, usually 

 from fourteen to twenty, equal, concentric, and regularly distributed rays. 

 The rays are, at the base, 0.4-0.9 [x thick and conical, either throughout or only 

 at the end, and then nearly cylindrical in their basal part. They are always 

 sharp pointed and more or less spiny. Sometimes the spines are too small to be 

 discerned as sucli and their i)resence is indicated only by a certain roughness of 

 the rays. More often, however, particularly in the larger oxyasters, the spines 

 are large enough to be clearly made out. The larger the spines, the fewer their 

 number. Some of the spines frequently form a verticil some distance below the 

 end of the ray. Oxyasters of this kind were chiefly observed in var. typica, 

 form A. The total diameter of the oxyasters is 7-17 [i. Those of var. typica 

 are a little smaller than those of the other two varieties. A few asters were 

 observed which appeared as transitions between these oxyasters and the acanth- 

 tylasters. 



