﻿22 OPHIURA HOLMESII. 



side a trifle shorter than outer side ; incision in disk includes three 

 plates ; first plate rudimentary, in form of segment of a circle, with its 

 curve inward, length to breadth, .8 : 1.2""°- ; second plate similar in form, 

 length to breadth, .8 : 1.8""°' ; third plate similar in form, length to 

 breadth, 1 : 3°"°- ; fourth plate of normal form, length to breadth, 

 1.2 : 3.2'"'°' ; about two thirds out on arm, plates proportionately longer, 

 outer corners much rounded, inner side shorter than outer so that 

 lateral sides slope ; length to breadth, 1 : 2"""- ; length of inner side, 

 1.4'°'°- ; close to tip of arm, plates wedge-shaped, the point inward, 

 length to breadth, .4 : .4°""', outer side slightly curved. Disk, granula- 

 tion of upper surface pretty close and regularj about one hundred and 

 eighty grains to a square mm. ; granulation of interbrachial spaces below 

 same as that above, and extending to bases of mouth-papilla3 excepting 

 side mouth-shields ; scales at base of arm completely covered by granu- 

 lation. Arm-spines short, stout, flat, rounded, varying very little in size 

 on the same joint ; upper ones, however, a little largest and longest. 

 Second and third joints, three spines, lengths to that of under arm-plate, 

 .8:1; fourth joint, fom* spines ; fifth joint, five s^jines ; sixth joint, six 

 spines ; seventh joint, eight spmes ; eighth joint, nine spines ; length of 

 uppermost and lowest spines to that of under arm-plate, .8, .8 : 1.2 ; a 

 few of upper spines are as long as 1°"°" ; about two thirds out on arm, 

 six spines, length to that of under arm-plate, .6:1; close to tip of arm, 

 four very short, stout spines, length to that of under arm-plate, .4 : .6. 

 Tentacle-scales : the two that belong to each tentacle continue till near 

 tip of anu, Avhere there is only one ; inside scale much like an arm- 

 spine, but broader and flatter ; outside scale shorter, being cut square 

 off at the end. Color, in alcohol : disk, above, with a dirty white patch 

 in centre ; rest of upper surface having a ground-tint of light yellowish- 

 brown (yellow ochre and vandjd^^e brown) slightly clouded with olive ; 

 arms above dirty olive, irregularly barred with same bro^\ii as ground- 

 tint of disk, but lighter ; bars include usually two or three joints ; lower 

 surface of disk and arms, uniform dirty white, with a brown tint just on 

 edges of disk ; arm-spines white. 



Variations. — The color is almost as variable as in 0. aj^jpresna. 

 Often the disk is nearly white above, while the arms are dark green, 

 and banded. According to drawings in possession of Prof Agassiz, a 

 common pattern in the living animal is a dark sap-green disk, with a 

 blotch of white in the centre, and arms banded with darker and lighter 

 green. Specimens with a disk of 14""°- have the under arm-plates more 

 octagonal and proportionately longer than among the larger. 



This species stands between 0. hrevispina and 0. olivacea; from the 

 former it is distinguished by proportionately thicker arms and stouter 

 disk, and by proportions of under arm-plates it is also a larger species, 



