ECHINODERMATA : ASTEROIDEA. 2OI 



the other hand, in Melonites and OHgoponis, the ambulacral 

 areas consist, respectively, of ten and four rows of plates. In 

 some of the Peris choechinidce the plates of the test are joined 

 by their edges, as in the common living Urchins ; but in others 

 (e. g., Lepidechimis] the plates overlap in an imbricating man- 

 ner, as in the recent Echinothuridce, and the test thus becomes 

 flexible. 



CHAPTER XIX. 



ASTEROIDEA AND OPHIUROIDEA. 



ORDER ASTEROIDEA (Stelleridd}. This order comprises the 

 ordinary Star-fishes, and is defined by the following characters : 



Fig- 97- The common Star-fish ( Uraster rubens), natural size, viewed from above. 



The body (fig. 97) is star-shaped or pentagonal, and consists 

 of a central body or " disc" surrounded by five or more lobes or 



