﻿84 OPIIIOCOMA ECHINATA. 



sides marked with lighter ; near the tip of the arm they are somewhat 

 lighter colored ; third and fourth arm-spines pure white below, above 

 white, with a broad central line of purplish brown ; tentacle-scales 

 white, with small purplish-brown spots, of which one is almost always 

 at the base of the scale. 



Variations. — The color, though varying in intensity, is usually as 

 described above ; sometimes, however, the upper surface of the disk 

 bears large patches of light grayish ; and, again, the whole animal may 

 be light gray, variously marked and clouded with brown ; this pattern 

 is seldom seen, except in the 3'oung. The granulation of the interbra- 

 cliial spaces below differs ; sometimes it completely covers the whole 

 area ; at other times, particularly among the young, it is confined to a 

 small triangular patch in the centre. A young one, with a disk of 9""-, 

 had arms 47™°- long ; the under arm-plates were a good deal broader 

 without than within, the outer side being strongly curved, and the 

 laterals re-enteringly curved ; the disk granulation was only partial 

 below, but perfect above, wdth about 90 grains to a square mm. ; there 

 were only thi'ee rows of tooth-papillae. 



O. echinata is the commonest of the West Indian Ophiuridse. It has 

 been found from low-water-mark to four fathoms ; usually on corals, 

 but often, also, on Gorgonia flahellum. The color does not change in 

 alcohol. The species is distinguished from O. Riisei by the shape of 

 the upper arm-spine and of the mouth-shields, and from 0. mthioj^s by 

 much narrower upper arm-plates. 



Miiller & Troschel state that Lamarck confounded several species 

 under the name of echinata, and among them a specimen from the 

 Antilles, brought by Plee, and which they make the type of their 

 O. serjjentaria. They exclude 0. echinata entirely, Avithout any reason 

 at all. The real original of Lamarck is a dried specimen in the Jardin 

 des Plantes, which, as I satisfied myself, was brought by Mauge from 

 Porto Rico in 1799. This is no other than the Ojihiura crassispina 

 afterwards described by Say, and identical also with Plee's specimen 

 above mentioned. 



