OPHIOZONA NIVEA. 9 



short angle within, at the corners of which begin the genital openings; 

 length to breadth, 1.1 : .7. Side mouth-shields large, long triangular, wide 

 without, and with straight sides, touching by their narrow ends within. 

 There are only two under arm-plates besides the first at the corner of the 

 mouth-slit. They are pentagonal, with an angle inward, and the lateral sides 

 re-enteringly curved ; length to breadth, .7 : .7. Beyond the third there are 

 no under arm-plates at all. Side arm-plates thick, and composing the entire 

 covering of the arm beyond the disk, excepting the small upper arm-plate. 

 Upper arm-plates very small, diamond shape, with an angle without and 

 within ; length to breadth, .4 : .5. Disk rather high and angular, covered by 

 closely soldered swollen plates, having decided grooves between them ; the 

 upper margin is occupied by two large rounded plates, one above the other, 

 touching the radial shield on either side ; the central space within the radial 

 shields is covered by a large pentagonal primary plate surrounded by two 

 irregular concentric rows of smaller and rounder plates. The interbrachial 

 space below is covered by five pieces besides the mouth-shield, to wit, three 

 lumpy plates, arranged in a triangle just outside the mouth-shield, and two 

 wide solid genital scales, which start at the inner corner of the genital open- 

 ings and touch the radial shields with their outer ends. Radial shields 

 roughly triangular, not much swollen, touching without, separated within by 

 a small wedge-scale and a large round plate ; length to breadth, 1.3 : 1.2. 

 Arm-spines very small, rounded, blunt ; two or three in number, and set in 

 a notch low down on the outer edge of the side arm-plate {Fig. S). Tentacle- 

 scales only on the second and third plates ; they are circular, and situated 

 at the inner corners. 



Color, in alcohol, white, clouded with pale brown. 



Hassler Expedition, one specimen ; Barbadoes, 100 fathoms. 



It differs from 0. validum Ljn. in wanting rudimentary under arm-plates, 

 and from 0. Lt/mani W. Thorns, in fewer and shorter arm-spines ; from both 

 these species it differs in the smaller radial shields, higher disk, and more 

 swollen disk-plates, which besides are differently arranged. 



Ophiozona nivea sp. nov. 



Outline figures, 85, 86. 



Special Harks. — Primary plates forming a conspicuous rosette in centre of 

 disk. A radiating line of plates in each upper interbrachial space. Lower 

 arm-plates hexagonal. 



