﻿114 OPIIIACTIS VIRESCENS. 



is much narrower at its base than it is a little way out. Disk-scales less 

 crowded and somewhat more regular than is common in the genus ; 

 there are about three parallel, radiating rows of rounded scales in the 

 nari-owest part of each interbrachial space ; a few short spines are scat- 

 tered here and there. Radial shields very straight along the side next 

 their neighboring shield, but much curved along the side next the 

 interbrachial space ; length to breadth, 1.1 : .6 ; they are separated for 

 nearly their whole length by a wedge of three long scales. Arm-spines 

 near base of arm, five ; two upper ones commonly thickest and largest ; 

 all of them very short, thick, rough, blunt, and a little tapering ; lengths 

 to that of under arm-plate, .5, .5, .4, .3, .2 : .5. Tentacle-scale flat, thin, 

 broader than long, rounded at the end, resembling a mouth-papilla, but 

 larger. Color, in alcohol : above, radial shields dark sap-green, tipped 

 on their outer ends with hghter ; rest of disk mottled with darker and 

 lighter sap-green ; arms banded and mottled with the same ; below, 

 mouth-parts and under arm-plates yellowish or greenish white. 



Variations. — The color varies in intensity and somewhat in pattern. 

 Sometimes the radial shields are not separated. A smaller one, with a 

 disk of 2.7°'°", had arms about four times as long ; the upper arm-plates 

 Avere proportionately not so wide ; the lower plates more roimded, and 

 inclining to an angular heart-shape ; the disk sj^ines were pretty nu- 

 merous, and longer than in larger specimens. 



0. virescens is very like 0. Krebsii, but differs in having the arm 

 suddenly swelled, a little way from the disk, instead of regularly taper- 

 ing ; the arm-spines, also, are rather more rounded, thicker, and blunter, 

 and the upper arm-plates proportionately a little wider, with a stronger 

 outer lobe. 



The first specimens were found at Realejo, in three fathoms of water, 

 and at Puntarenas, by Dr. Orsted ; others have since been sent from 

 Cape St. Lucas by Mr. Xantus. 



LIST OF SPECIMENS. 



Whence obtained. 



Museum of Comparative Zoology. 

 I IIGG I 1 I Cape St. Lucas, Cal. | | J. Xantus. | Alcoholic 



Smithsonian Institution. 

 11C6 I • • I 5 I Cape St. Lucas, Cal. I I J. Xantus. I 



Alcoholic 



