278 



THE OCEAN WORLD. 



The family of Ophiuradae is divided into two great sections : that of 

 the Ophiura, which comprehends several genera, amongst others that 

 which gives its name to the family, and that of the Euryalina or 

 Asterophytes. 



The family of Ophiuradae constitute a group distinguished hy their 

 five simple, articulated, very mobile, and non-ramified arms, which 



Fig. 110. Ophiocoma Russei (Lutken), natural size. 



are attached to a small disk or shield plate, with flexible thread-like 

 cirri between the rays. Ophiura natta is very common, and has been 

 known from very early times in European seas. It is of a greenish 

 colour, with transverse bands, which become more obscure upon the 

 arms as the distance from the disk increases. This disk is from six to 

 seven-eighths of an inch in size, the upper part covered with unequal 

 plates, in shape like tiles ; the arms are four times the length of the 



