﻿AMPIIIURA URTICA. 



129 



angle directed inward ; outer angle truncated, and making a slight 

 peak ; other angles slightly rounded ; length to breadth, .5 : .5. Side 

 mouth-shields not meeting within. Uj^per arm-plates irregular oval, 

 outer side less curved than inner side ; length to breadth, .5 : .7. Under 

 arm-plates scarcely touching each other ; inner one five-sided, the rest 

 nearly square, with a strong notch in the outer side ; length to breadth, 

 .4 : .4. Scales of disk fine and even, about 140 to a square mm. ; some 

 of those near margin of disk bearing very fine prickles on their edges. 

 Primary plates not conspicuous. Radial shields elongated oval, tapering 

 within, joined for their whole length ; length to breadth, 1 : .5. Arm- 

 spines three, about as long as the joints, delicate, sharp, regularly 

 tapering. Tentacle-scales two, both of them small and delicate. Color, 

 in alcohol : vipper and under surface of disk dark greenish-gray, with a 

 margin of light ; arms light straw-color. 



Variations. — The mouth-shields vary in shape to an unusual degree ; 

 sometimes they have a strong peak without, and again none at all ; 

 they may be nearly rectangular, or almost oval, and some are not for 

 from round. The under arm-plates may be more or less pentagonal ; 

 but, in the adult, most of them are nearly square. The young, with a 

 disk 2.5""°- in diameter, have the under arm-plates pentagonal, with a 

 deep notch in their outer side, and separated by the side arm-plates ; 

 they have also, on the back of the disk, a conspicuous rosette of round 

 primary scales. 



This species differs from A. occidenfalis in its notched under arm- 

 plates, sharp spines, and prickly scales of the disk. It is a somewhat 

 aberrant species, and by its prickly scales approaches Opliioenida sca- 

 hriuscula. 



LIST OF SPECIMENS. 



Whence obtained. 



Museum of Gomparalive Zoohr/y 

 243 I 105G I 1 I Puget Sound. | | Dr. Kennerly. | Alcoholic. 



Smitlisonian Institution. 



105G I . . I 5 I Puget Sound. 1 I Dr. Kennerly. I Alcoholic. 



1041 . . 6 Puget Sound. Dr. Kennerly. " 



