50( 



ECHI] 



l OPHIUROIDEA 



Ophiopteron is probably a swimming Ophiuroid, as the lateral 

 spines of each segment of the arm are connected by a web of 

 skin. 



Order III. Cladophiurae. 



These, like the Streptophiurae, have the power of rolling the 

 arms in a vertical plane, but the articulating surfaces of the 

 vertebrae are well -developed and saddle -shaped. The dorsal 



Fig. 222. Aboral view of young Astrophyton linckii, slightly enlarged. 

 (From Wyville Thomson.) 



surface of the disc and arms is covered with a thick skin with 

 minute calcifications. Upper-arm plates wanting. Eadial plates 

 always present, though occasionally, represented by lines of scales. 





