ECHINARACHNIU8. 



107 



chUdren who livenear 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 their 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 



Fig. 139. 



disk is so fiat, 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 Toxopneustes is 

 sometimes called. But upon closer examination the delicate am- 

 bulacral 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 moi-e 

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



Fig. 139. Eohinaraohnius, seen from above, with tlie spines on part of the shell ; a ambulacral zone, 

 j interambulncral zone. 



