110 



THREE CRUISES OF TIIE " BLAKE. 



Besides the peculiarity of branching arms (Astrojihyton coe- 

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

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

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

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

 skin (Ophioc?*eas spinulosus, Fig. 389). The typical Ophiu- 

 ridse have a well-marked central disk covered with plates or 

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

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



Fig. 390. — Ophiozona nivea. |. 



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

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



■ ■ .->.\ /; 



Fig 391. — Ophiophyllum petilum. \. 



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

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



