356 A. JE. Yerrill — JVbrth American Ophiuroidea. 



covered and concealed by thick cuticle ; in having the under arm- 

 plates in contact ; and in having two tentacle-scales. 



The arm-spines are short, nearly equal. Radial shields naked, 

 ovate, and separate. 



Ophiochondrella squamosus (Lym.). 



02}hiochonclr'us squamosus Lym., Bull. Mns. Comp. Zool., x, p. 275, pi. vii, 

 figs. 108-110, 1883. 



The disk-scales are thick, swollen, irregular. Arm-spines eight, 

 tapered. Oral papillae three, small, spaced. Tentacle-scales minute, 

 rounded. West Indies, 250 fathoms, Blake Exped. 



Ophioclxondrus Lyman. 



Bulletin Miis. Comp. Zool., i, p. 328, 1869; Voy. Challenger, p. 247, 1882. 

 Type, O. convoliitus Lyman. 



The characters given to this genus by Mr. Lyman should be modi- 

 fied by adding that there are two or three nearly vertical j^lates at 

 the base of the arm, supporting the ends of the radial shields, so that 

 the edge of the disk is considerably raised above the arm, making a 

 sharp angle with it. The radial shields are still more strongly sup- 

 ported by an elongated genital plate, running up each side of the 

 genital slits and joining the radial shields. 



Ophiochondrus crassispinus Lyman. 



Ophiochondrus crassispinus Lyman, Bulletin Mus. Comp. Zool., vol. x, p. 275, 

 1883. 



Several specimens from the Blake Exp., Station 232, 88 fath., oif St. 

 Vincent, were sent to the Yale Museum by Mr. Lyman under the 

 name of 0. convolutiis, under which they are also evidently recorded 

 in Mr. Lyman's lists of 1883. 



-These, on careful study, appear to belong to 0. crassispinus, as 

 defined and figured by Mr. Lyman. The latter was. described from 

 a single specimen, from 229 fath., Blake Exp. 



They have three acute, conical, oral jjapillae, exclusive of the odd 

 terminal one. The oral shield is small, thick, pear-shaped, with an 

 acute proximal angle ; arm-spines six or seven, short, nearly equal. 

 A very small acute tentacle-scale is usually present in the larger 

 specimens. Upper arm-plates on proximal part of arm, except two 

 basals, are nearly quadrant-shaped with -the outer edge convex and 

 the lateral angles acute ; distally they become more nearly trian- 

 gular, with the sides a little convex. 



