chap, xvii.] OPHIUROIDEA. 447 



nat., p. 34; also Gauthier, Com-ptes rendus Ass. fr. pour Vav. Sci., Toulouse, 1887, 

 and other references given by these authors.] 



Ophiuroidea. 



Individuals with various numbers of arms are often seen, 

 especially in the genera Ophiothela, Ophiocoma, Ophiacantha and 

 Ophiactis, and in many of the species there are most usually 

 six arms. In these forms the evidence as to Meristic Variation 

 is complicated by the circumstance that in several of them change 

 in the number of arms may take place in the ontogeny, by division 

 and subsequent regeneration (see note on p. 433). 



