ECirLNAllACHNIUS. 



107 



children who live near sandy beaches, they are well known as 

 "sand-cakes" (Fig. 139), and indeed they are so flat and 

 round, that, when dried and deprived of then- bristles, they look 

 not unlike a cake with a star-shaped figure on its surface. (Fig. 

 139.) When first taken from the water they are of a dark 

 reddish brown color, and covered with small silky bristles. The 



Fis. 139. 



disk is so flat, being but very slightly convex on the upper side, 

 that one would certainly not associate it at first sight with the 

 common spherical Sea-urchin or Sea-egg, as the Toxopncustes is 

 sometimes called. But upon closer examination the delicate am- 

 bulacra! tubes or suckers may be seen projecting from along the 

 line of the ambulacra, as in the spherical Sea-urchin ; and though 

 these ambulacra become expanded near the summit into gill-like 

 appendages, forming a sort of rosette in the centre of the disk, 

 they are, nevertheless, the same organs, only somewhat more 

 complicated. When such a disk is dried in the sun, and the 



Fig. 139. £chinarachnius, seen from above, vith the spines on part of tlie shell ; a uujbulucral zoae, 

 i interambulacral zone. 



