MUSEUM OF COMPARATIVE ZOOLOGY. 341 



to breadth (3d joint from disk) .8 : 1.1. Towards the tip of the arm they 

 are triangular, with the outer side curved, and the apex directed inward. 

 Disk covered with fine scales and radial shields ; the former nearly hidden 

 by the skin, except on the lower surface. Radial shields very narrow, and 

 joined for their whole length ; pointed within, swollen at their outer ends ; 

 length to breadth 2 : .5. They are sunk below the puffy surface of the disk, 

 and are placed at the inner point of a notch in the disk, which exists over 

 each arm ; this inlacing of the soft disk is as deep as one or two arm-plates, 

 portions of which are thus exposed, together with their spines, which are bent 

 outward by the overlying disc margin. The sides of the notch are formed 

 of an upward prolongation of the genital plate. The entire disk is pretty 

 evenly beset with very slender, sharp spines about. G mm. long. Genital 

 slits with a distinct genital plate, whose edge is visible for its whole length, 

 and which turns over and widens at each end, especially at the outer, where 

 it runs upwards above the arm. Arm-spines, outside the disk and near base 

 of arm, nine, whereof the two lowest are stout, rounded, pointed, and 

 longer than the others ; the next four flattened, tapering, and most slender ; 

 the three highest also flattened and tapering, but rather stouter ; lengths to 

 that of under arm-plate (10th joint) 1.1, 1.1, .9, .7, .7, .7, .7, .7, .7 : .8. On 

 the second joint only two spines ; on the other joints, within the disk, about 

 three. Near tip of arm, four spines, lowest longest, slender, tapering, 

 rounded, rather longer than the joint. Tentacle scales two, — one short, 

 sharp, tooth-like and about .4 mm. long (10th joint), standing on the edge 

 of the side arm-plate ; the other slender, sharp, spiniform, and borne on the 

 lateral edge of the under arm-plate; length (10th joint) .6 mm. The 

 former of these scales is found to the very tip, where it takes on the form of 

 a pointed oval ; but the spiniform scale is only seen on the first third of the 

 arm, where it disappears, having grown gradually shorter and smaller. 



Color, in alcohol, dull olive for the disk ; arms, light olive brown. 



Three specimens, in 79 fathoms, off Alligator Reef; and two arms, in 40 

 and in 117 fathoms, off Carysfort Reef. 



Ophiothamnus Lyman, gen. nov * 



Teeth : no tooth-papillcc : mouth-papilla?, of which the outer is much the 

 broadest. Side mouth-shields long and stout, extending outside the mouth- 

 yhields, and making, with them, a conspicuous raised pentagon. Side arm- 

 plates Large, meeting above and below, and bearing slender, rough spines 

 on their sides. Disk puffed, and overlying the bases of the arms, covered 

 with scales and radial shields, which are beset with spines. 



This genus, by its arm-plates and chewing apparatus, is allied to 



* 5'^ts, a snake; 0J.;xvo<;, a thicket. 



