﻿OPHIOCOMA INSULARIA. 89 



Ophiocoma insularia Lyman. 



Oph'wcoma insularia Lymax. Proceed. Boston See. Nat. Hist., VIII. p. 80. 



Sjjecial 3Iarks. — Lower spines longer than the upper ; arms flat, 

 about four times as long as diameter of disk ; under arm-plates regular, 

 and about as long as broad ; interbrachial spaces below closely granu- 

 lated. 



Descrijition of a SiJecimen. — Diameter of disk, ,30""°' ; width of arm 

 without spines, 4.5"""- ; length of arm, 125""°-. Mouth-papilla3, six on 

 each side ; under the teeth there cannot be said to be any mouth- 

 papillas, because the tooth-papilljB, which sometimes are as many as 

 twenty, extend downwards and outwards, growing smaller and smaller, 

 till they nearly reach the inner end of the mouth-shield. Teeth four, 

 flat and squarish, upper one smallest. Mouth-shields about as long as 

 broad, much rounded, without straight lines ; length to breadth, 2.8 : 2.5. 

 Side mouth-shields small, triangular, lying entirely on the sides of the 

 mouth-shields. Under arm-plates about as broad as long, bounded with- 

 out by a curve, and within by a short inner side and two inner laterals ; 

 length to breadth (sixteenth plate), 2 : 2. Upper arm-plates even and 

 regular, much broader than long, bounded without by a clean curve, 

 and within by an inner side and two inner laterals ; length to breadth, 

 2 : 4. Granulation of the disk extremely close and fine above and 

 below, and extending even to the outer corner of the side mouth- 

 shields ; about 45 to a square mm. Arm-spines rather short, little 

 tapering, blunt, a good deal compressed ; on the first few joints beyond 

 the disk, four, very rarely indeed five ; farther out, three ; they do not 

 alternate three and four, as is seen in many other species ; lengths to 

 that of under arm-plate, 3, 3.1, 3.6, 3.5 : 2. Tentacle-scales two, large 

 and regular, much longer than broad. Color, in alcohol : above, deep 

 umber, almost black ; below, interbrachial spaces the same ; arms a 

 little lighter. 



Variations. — A young specimen, with a disk of 9.5°"°-, had arms 

 ggmm. ^QQg . ^j^g mouth-shields were narrower than in the adult, the 

 color was paler, and the tips of the arms were cross-barred with white. 

 A very large specimen, with a disk 33""°- in diameter, had arms 155""°- 

 long ; the proportion of the ann-spines to the under arm-plate was 3.5, 

 3.5, 3.7, 3.7 : 2 ; the upper spines were greatly flattened, and were cut 

 square off at the end. Some well-grown individuals have cross-bars of 

 light-brown towards the end of the arm. 



