444 bulletin: museum of comparative zoology. 



cealed by the smooth uniform layer of fine granules, about 150 to a 

 square millimeter. Radial shields entirely concealed. Upper arm- 

 plates tetragonal, becoming almost triangular at very tip of arm, 

 where they are as long as wide; on basal portion of arm they are 3-4 

 times as wide as long and cover the entire dorsal surface of arm. 

 Basal half of arm distinctly keeled, though the keel is low and rounded. 

 Interbrachial areas below uniformly covered with the fine coat of 

 granules of disk. Genital slits four in each interbrachial area. Oral 

 shields triangular with very rounded angles, a trifle wider than long. 

 Adoral plates ver.v small, bare, at distal corners of oral shields. Oral 

 plates completely concealed by granules. Oral papillae 9-10 on each 

 side, the two distalmost and the most proximal one, largest; far up 

 in the mouth-slit, on the side of each jaw is a conspicuous pointed 

 papilla as large as the largest of the oral papillae. Teeth about five. 

 No true tooth-papillae. Under arm-plates at first hexagonal with 

 strongly convex distal side which soon develops angles, making the 

 plate octagonal; on basal half of arm, the plates are much wider 

 than long; distally they become tetragonal with rounded corners 

 and ultimately they are longer than wide. Side arm-plates low and 

 small; each carries 5 rather stout, flat, blunt arm-spines, of which 

 the uppermost is smallest, about half as long as side arm-plate, and 

 the lowest is conspicuously largest, much exceeding the plate; on 

 distal part of arm there are of course only 4, and then 3 arm-spines. 

 Tentacle-scales 2, the inner narrower than the outer and very much 

 longer, commonly longer than the side of the under arm-plate which 

 it adjoins; outer scale flat and truncate, overlying the base of the 

 lowest arm-spine. Color (dried): — light and dark brown, with a 

 slight grayish cast; disk with dark blotches on a lighter background; 

 arms more or less distinctly banded; under surface of disk fawn-color, 

 of arms nearly white, except distally. 



Station 4643. Galapagos Islands: Hood Island, 5 miles southwest 

 of Ripple Point. 100 fms. Bott. temp. 67.2°. Brk. sh., glob. 



Five specimens. 



This fine species, one of the most easily recognized in the genus, is 

 indeed an interesting discovery. It resembles 0. claps of the West 

 Indian region more nearly than it does any other species, but is at 

 once distinguishable from that form by the small number of arm- 

 spines. As a characteristic species of the Galapagos region, Ophio- 

 dcnna pentacantha will probably be entitled to high rank. 



