﻿66 OPHIOZONA IMPRESSA. 



several smaller scales ; scales of interbrachial spaces below, smaller and 

 thinner than those above. Arm-spines five, short, moderately stout, 

 tapering, rounded, uppermost one shortest, two lowest ones rather the 

 stoutest ; lengths to that of under arm-plate (seventh joint), .6, .7, .7, 

 .9, .9 : 1 ; near end of arm, only three spines ; and even near its base, 

 there are often only four. Tentacle-scales two, stout, longer than broad, 

 set close to each other, and forming together an oval. Color, in alco- 

 hol : above, disk-scales and arm-plates vandyke-brown, some of them 

 edged or mottled with white ; arms irregularly banded with burnt 

 umber ; below, arms and mouth parts faint yellowish-brown ; interbra- 

 chial spaces nearly white, with a tinge of greenish. 



Variations. — The larger disk-scales are in some specimens more 

 prominent and distinct than in others ; occasionally there are only 

 three, instead of five, radiating rows of larger scales, in each interbra- 

 chial space above. The color, in alcohol, varies a little in intensity. 

 The proportions of the arms to the disk may be as 9.2 : 36, 11 : 41, 

 12.5 : 66, 13.2 : 51, 14 : 57, or 15.5 : 64. 



0. impressa has been taken at St. Thomas, in from one to four feet 

 of water, on a sandy bottom, or on corals (A. H. Riise) ; also on the 

 coast of Florida (Professor Agassiz, Mr. Wurdeman). It may be dis- 

 tinguished from 0. jKiciJica by having longer arm-spines, which are not 

 of equal lengths. 



LIST OF SPECIMENS. 



Whence obtained. 



Museum of Comparative Zoology. 



St. Thomas, W. I. 

 West Indies. 



Smithsonian Institution. 



St. Thomas, TV. I. 

 St. Thomas, AV. I. 

 St. Tliomas, W. I. 

 St. Thomas, W. I. 



A. II. Riise. 



University Museum, 



Copenhaijeu. 

 Prof. Agassiz. 



A. H. Riise. 



A. II. Riise. 



A. II. Riise. 



A. H. Riise. 



