﻿166 



OPHIOTHRIX VIOLACEA. 



with a pvirplisli tint ; below, chewing ajoparatus yellowish, mouth-shields 

 white, speckled with jourplish blue ; imder arm-plates the same, but, in 

 addition, bordered with pale purplish-blue ; interbrachial spaces finely 

 mottled with white and purplish blue. 



Variations. — The color differs chiefly in being darker or paler ; in 

 the former case, the white spots on the upper arm-plates may be oblit^ 

 erated, and even the longitudinal Avhite line become quite faint. Often 

 the imder arm-plates are white through the centre, while the lateral 

 sides are dark blue. The proportions of disk to arms present such 

 differences as the following : 9 : 53, 10 : 44, 7.5 : 42, 5 : 23. Dr. Liitken 

 gives a measurement as high as 10 : 80. The average of seven meas- 

 urements of the length of under arm-plates compared to that of longest 

 arm-spines, near base of arm, was .7 : 3.1 ; the extremes were .6 : 3 and 

 .8 : 3.2. The spines on the upper surface of the disk vary somewhat in 

 number and also in the length of their thorns ; those below vary very 

 much in number, being sometimes closely set, sometimes almost want- 

 ing, sometimes thorny, sometimes smooth. The side mouth-shields 

 sometimes quite meet within. 



This species is apparently much more common at St. Thomas and the 

 neighboring islands than in Florida. Certainly in Key West it is com- 

 paratively very rare. It is distinguished from other species as follows : 

 from 0. Orstedii, by short, forked spines of disk, and different pattern 

 of color in alcohol ; from 0. Suensonii, by short, forked spines of disk, 

 and a white median line along arm, instead of a dark one ; from 0. 

 lineata, by more slender and numerous arm-spines, and by short, forked 

 spines of disk ; from O. angulata, by greater size (7'""'' diameter of disk, 

 corresponds in O. angulata to about lO"""' in 0. violacea), by fewer 

 long spines on disk, and by a much darker pattern of color, when in 

 alcohol. 



LIST OF SPECIMENS. 



Whence obtained, - 



CO 1^1 



1017 

 lOlG 

 1159 



Museum of Comparative Zoology. 



Jeremie, Havti. 

 St. Thomas, W. I. 

 Rio Janeiro. 

 West Indies. 

 Charlotte's Harbor, Fla. 



Smithson 

 West Indies. 

 Rio Janeiro. 

 St. Tliomas, W. I. 

 St. Tliomas, W. I. 

 St. Thomas, W. I. 



Dr. D. F. Weinland. 

 A. II. Riisc. 

 Univ.Mus.Cop'hagen 

 Univ.Mus.Cop'hagen, 

 G. Wurdeman. 



Univ.Mus.Cop'hagen. 

 Univ.Mus.Cop'hagen. 

 A. H. Riise. 

 A. H. Riise. 

 A. H. Riise. 



Dried. 

 Alcoholic 



