THREE CRUISES OF THE “BLAKE.” 
110 
Besides the peculiarity of branching arms (Astrophyton cæ- 
cilia, Fig. 388) which distinguishes some of the genera, the As- 
trophytidee have characteristic joints in the arm-axis, which sepa- 
rate them from the Ophiuride. They are also usually covered, 
not by conspicuous plates of lime carbonate, but by a leathery 
skin (Ophiocreas spinulosus, Fig. 389). The typical Ophiu- 
ride have a well-marked central disk covered with plates or 
scalés, and from it radiate five arms encased in four longitudinal 
rows of plates (Ophiozona nivea, Fig. 390). The side arm- 
Fig. 390. — Ophiozona nivea. 4, 
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. 4. 
angle (Ophiocamax hystrix, Fig. 392). There is an almost 
endless variety in the shape, consistency, number, and size of 
