1918 Hush: on Echinoderms 33 



Family ASTEROPIDAE 

 Genus Dermasterias 

 Rays 5, short, broad ; disk broad, thick, not distinguished from rays ; 

 entire surface covered with thick soft lubricous skin. Dorsal ossicles 

 concealed by skin in living specimens, showing in dried specimens, round- 

 ish, imbricated; pedicellariae small, valved, on dorsal surface. 



1. Dermasterias imbricata (Grube) Perrier. Leather Star 



Asteropsis imbricata Grube; Dermasterias inermis Perrier. 

 Rays 5, broad, tapering, usually short; disk large, plump; surface 

 smooth and lubrious in life due to thick soft skin. Dorsal ossicles roundish, 

 lobed, connected by other small ossicles ; ossicles of interradial region 

 imbricated ; interactinal plates ovate, rows parallel to ambulacra and im- 

 bricated; adambulacral spines 2 to a plate, terete distally; small valved 

 dermal pedicellariae may occur; large ventral pedicellariae often present 

 and may take place of outer adambulacral spines. — Rather numerous, in 

 deep water and along tide line. 



Glass Ophiuroidea 



KEY TO ORDERS 



A. Rays unbranched ; lateral plates of rays spine-bearing ; ambulacral 

 ossicles articulating by means of processes and pits. 



Zygophiura (p. 33) 



AA. Rays branched or unbranched; lateral plates of rays not spine- 

 bearing; ambulacral plates articulating by means of hour-glass-shap^'^ 

 surfaces. Cladophiura (p. S5) 



ORDER ZYGOPHIURA 



KEY TO GENERA 



A. Ray-spines short, 1/4 t'^^ width of the rays, parallel to ray-axis. 



Ophiura (p. 34) 

 AA. Ray-si^ines long, -y^ the width of the rays, at right angles to ray- 

 axis. 

 B. Median dorsal plates of rays surrounded by a series of smaller 

 plates; length of arms less than 10 times tlie diameter of tlio disk. 



Ophiopholis (p. 31-) 

 BB. Median dorsal plates of rays not surrounded by a series of smaller 

 plates; length of arms more than 10 times the diameter of the disk. 

 C. Oral papillae 3, equal, arranged in a regular series. 



Amphiodia (j). Si) 

 CC. Oral papillae 4, unequal, arranged in a discontiiuious series. 



Amphiopli's (p. 31) 



