382 RADIATA. 



quite flat beneath, but slightly convex on the upper 

 surface. The structure is the same as before ; but 

 the spines appear to the naked eye only as very 

 minute hairs ; but when magnified are found to be 

 of most elaborate workmanship, each having a move- 

 able socket-joint. In the genus Clypeaster,* the 

 round outline is changed for a five-sided figure ; 

 the angles of which in succeeding species project 

 more and more, and the spaces between become 

 more and more indented, till we arrive at the Star- 

 fishes (Asterias^). 



The skin of the Star-fishes does not assume a 

 shelly character, being merely of a dense and tough 

 leathery texture. The common form is that of 

 a star with five pointed rays, as is shewn in that 

 species with which our coasts are familiar, the Sea- 

 star, or Five-finger (A. Rubens). It does not, how- 

 ever, materially differ in structure from the Sea- 

 urchin ; but the minute pieces of solid matter do 

 not take the same ' regularity of form, nor are they 

 so accurately joined to each other. The surface 

 is studded with irregular projections, causing a gene- 

 ral roughness, which probably represent the spines. 

 Along the centre of each ray, on the under surface, 

 run the furrows studded with minute holes, from 

 which project sucker-feet, as in the above genus. 

 The mouth, in the centre of the under side, is sur- 

 rounded by a bony ring, but is destitute of teeth. 

 Yet the Star-fish is very voracious, swallowing small 

 shelled Mollusca whole, and afterwards disgorging the 



* Clypeus, a shield, and aster, a star. t Their Greek name. 



