22 OPHIURA IIOLMESIL 



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, 

 2 j.mra. . (.|Qgg ^Q ^ip of r^i-jj^^ plates wedge-shaped, the point inward, 

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

 tion of upper surface pretty close and regular, 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-papillas 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, four spines ; fifth joint, five spines ; sixth joint, six 

 spines ; seventh joint, eight spines ; 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 l"""*' ; about two thirds out on arm, 

 six spines, length to that of under arm-j^late, .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 tiU near 

 tip of arm, where 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 vandj'ke brown) slightly clouded with olive ; 

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

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

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

 edges of disk ; arm-spmes white. 



Variations. — The color is almost as variable as in 0. appressa. 

 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 O. brevispina and O. 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. 



