302 



ERYLUS ROTUNDUS. 



fourteen rays 12-19 in diameter. The rays are, at the base, 0.5-2.4 p. thick 

 and taper distally. At their ends they are usually thickened to an acanthtyle, 

 rarely simply rounded off. The transverse diameter of the acanthtyle (rounded 

 end) is, inclusive of its spines, 0.5-4 [i. The basal part of the rays is always 

 quite smooth. This smooth part may be quite short, or it may extend right up 

 to the acanthtyle (the rounded, spiny end). Acanthtylasters with rays smooth 

 right up to the acanthtyle have been observed chiefly in var. typica, form A. 

 Usually the proximal one to two thirds of the rays are spineless, the remaining 

 distal part being either rough or provided with smaller or larger spines. The 

 larger the spines, the fewer their number. Frequently an increase in the size of 

 the spines towards the end of the ray is noticeable. The acanthtyle is covered 

 with numerous, fairly large spines. Most of the spines appear to be conical and 

 pointed, but in var. rnegarhahda, form A, acanthtylasters with cylindrical spines, 

 rounded at the end, have also been observed. The spines of the acanthtyle are 

 usually somewhat recurved. The proximal spines are usually directed more or 

 less obliquely backward, the distal obliquely upward and outward. On the 

 whole the acanthtylc-spines have the appearance of short hair combed down 

 in all directions from the apex. The spines on the other parts of the rays are 

 vertical or, more rarely, directed obliquely outward. 



DIMENSIONS OF ACANTHTYLASTERS. 



Acanthtylasters 



Erylus rotund us 



var. 



megarhabda 



var. typica 



var. 

 cidaris 



all varieties 



A 



B 



all forms 



A 



B 



C 



D 



all forms 



South Molokai 



Kauai 



South Molokai 



Kauai, dark specimen 



Kauai, light specimen 



Northeast Hawaii 



with two 

 rays 



total diameter, 

 /' 



















24 



24 



basal thickness 

 of rays, /< 



















1.5 



1.5 





diameter of 

























acanthtyle 



















3.3 



3.3 





(roinided end), /j. 























