﻿28 OPIllURA CINEREA. 



plates four-sided, outer side curved, and longer than inner side, length 

 to breadth, .6 : .8. Disk : above, granulation very even, close, and fine, 

 about one hundred grains to a square mm. Radial shields regular oval, 

 standing nearly opposite outside lines of arms, quite smooth, length to 

 breadth, 1.6 : 1.2 ; between radial shields and base of arm there are 

 sometimes one or two rounded scales ; edges of incision in disk lined 

 with small, thick, overlapping scales, varying in length from .2 to I""' ; 

 at inner angle of incision these scales form a single row, but at outer 

 angles they make a triangular cluster of six or seven rows, and are 

 continued, over edge of disk, to its under surface, and reach as for as 

 outer pair of genital slits ; they make, on under surfece of disk, three 

 irregular rows, interspersed with grains ; all other parts of interbrachial 

 spaces, except mouth-shields, covered with a close granulation, quite to 

 the bases of the mouth-papillae. Genital slits, length of outer pair, 1.4""°-, 

 of inner pair, 1.2°"°-. Arm-spines short, stout, increasing in size from 

 uppermost one to lowest, which is considerably the largest ; upper ones 

 more pointed and rounded, lower ones more blunt and flattened ; second 

 joint, two spines, length to that of lower arm-plate, .8, 1.2 : 1.2 ; seventh 

 joint, five spines ; eighth joint, six or seven spines ; tenth joint, eight 

 spines, .4, .6, .6, .8, .8, .8, 1, 1.2 : 1.2 ; about two thirds out on arm, six 

 spines ; near tip of arm, four very short, thick, pointed spines. Tenta- 

 cle-scales two, continued close to tip of arm ; inside one somewhat larger 

 and longer, thin, cleanly rounded at end ; outside one similar, but cut 

 off square at end ; length to that of under arm-plate near base of arm, 

 inside scale, .8 : 1.2 ; outside scale a trifle shorter. Color, in alcohol : 

 disk, above, bro^vnish gray (burnt umber and neutral tint), with fine 

 specks of umber brown, each radial shield Ijounded by a line of umber 

 brown ; below, interbrachial spaces light brownish-gray, with a few 

 specks of light umber-brown ; mouth-shields and angles of mouth light 

 umber-brown ; mouth-papilla? white ; under and side arm-plates like 

 interljrachial spaces below, but variously clouded, and marked with 

 white and with shades of brown ; arm-spines white, with a bro-\vn line 

 round the base ; upper arm-plates same as upper side of disk, but vari- 

 ously Uned and marked with dark-brown ; the breaks in the plates are 

 marked with this color. 



Variations. — This species is always sober in its colors, the chief 

 variation being in intensity ; old specimens are sometimes nearly black, 

 while others are dark gray, speckled with umber brown. The young 

 might well be mistaken for another species. A specimen wdth a disk 

 of O.S""' had arms 32""°-. Upper arm-plates regular and unbroken, cov- 

 ering only a part of upper surfoce of arm, their inner side much shorter 

 than the outer ; seven arm-spines ; sixteen to eighteen mouth-papilla? ; 

 radial shields large, oval, length 1.5""° . Color, above, very light brown. 



