ECHINODERMATA—ASTEROZOA. 571 



O. asper Miller, O. confragosus Miller and O. demissus Miller, 

 from the Keokuk of Missouri, and O. ftexilis Meek and Worthen 

 (Fig-. 1909) from the Keokuk of Indiana. 



11. Ophiure^, with simple arms, generally encased by four 

 series of plates, the upper and lower of which (scutella dorsalia, 

 ventralia) are generally smooth, while the lateral or adambulacral 

 plates are generally furnished with movable spines. American 

 representatives are : Protaster whiteavesianus Parks, from the 

 Trenton of Kirkfield, Ontario ; P. granuliferus M. and W., from 

 the Cincinnatian of Ohio; Eugaster logani Hall, from the Ham- 

 ilton of New York; Aganaster gregarius (Meek and Worthen), 

 from the Keokuk of Crawfordsville, Indiana; Ophioglyphabridger- 

 ens^is (Meek), from the Cretacic of Montana; and Amphitura 

 sanctcF criicis, Oswold, of the Santa Magarita formation (Mio- 

 cenic) of California. 



Class 2. ASTEROIDEA. 



The Asteroids, or star fish, have simple arms, which are pro- 

 longations of the central disk, containing prolongations of the 

 digestive cavity and the generative organs. The ventral border 

 of the arms is marked by the amhulacral groove, formed by two 

 rows of ambulacral ossicles, 

 which meet in the center. Later- 

 ally these are bordered by the 

 adambulacral or interambulacral 

 plates, which generally bear mov- 

 able spiiies. Between the ambu- 

 lacral ossicles are grooves for 

 the passage of the tube feet or 

 ambulacra, either in a single or 

 a double row on each side of the 



,. ,. /T^i 1 1 r Fig. IQIO. Stenaster salteri, V 2. (Af- 



median Ime. I he dorsal surface ^ ^.... ^ r^ t^ t^ ttt \ 



ter Bilhngs, Can. Org. Rem., Dec, 111.) 



is formed by a network of os- 

 sicles, often with spines and other appendages. A madreporic 

 body is typically situated dorsally in one of the interrays, but in 

 the Encrinasterise is on the oral side. 



Two subclasses are recognized: 



I. Encrinasteri^, comprising most of the Palaeozoic forms and 



