110 



THREE CRUISES OF THE " BLAKE.' 



Besides the peculiarity of branching arms (Astrophyton coe- 

 cilia, Fig. 388) which distinguishes some of the genera, the As- 

 trophytidse have characteristic joints in the arm-axis, which sepa- 

 rate them from the Ophiuridae. They are also usually covered, 

 not by conspicuous plates of lime carbonate, but by a leathery 

 skin (Ophiocreas spinulosus, Fig. 389). The typical Ophiu- 

 rida3 have a well-marked central disk covered with plates or. 

 scales, and from it radiate five arms encased in four longitudinal 



' O 



rows of plates (Ophiozona nivea, Fig. 390). The side 



arm- 



Fig-. 390. Ophiozona uivea. 2. 



plates bear spines, which may lie close along the arm (Ophio- 

 phyllum petilum, Fig. 391), or stand out from it at a strong- 



391. Ophiophyllum petilum. 



angle (Ophiocamax hyslrix, Fig. 392). There is an almost 

 endless variety in the shape, consistency, number, and size of 



