ERYLUS SOLLASII. 

 DIMENSIONS OF TRIAENES. 



281 



This appears as a rudiment of a third ray. Most of the spines are conical, 

 straight, and vertical, some conical and recurved (Plate 2, fig. 1), some irregu- 

 lar, cylindrical, terminally rounded or even thickened, and occasionally lobose 

 at the end. 



The acanthtylasters measure 10-38 /i in diameter. Their size is in inverse 

 proportion to the number of their rays. To obtain a clearer insight into this 

 correlation I measured (and counted the rays of) 207 of them and took the 

 means of the diameters of those with the same ray-numbers. There is no 



