Arduridse in the U. S. National Museum. 



47 



The abdomen is elongated and slender ; the first and second segments 

 arc clearly defined ; a third is indicated by a deep and irregular constric- 

 tion ; the terminus is incised. 



A large number of specimens show a light line running along the me- 

 dian line of the dorsal surface and along the sides in line with the eyes. 

 The dark colored or shaded portions of the surface are made up of nu- 

 merous black spots. Now and then a large female is veiy light in color, 

 the lines being but slightly indicated. 



The largest specimens are IS mm. in length. 



Station 3252, lat. 57° 22' 20" N., long. 164° 24 / 40/' \V. ; depth L'it.l 

 fathoms; specimens very numerous. (Type, No. 20529, U. S. N. M.) 

 Station 3253, lat. 57° 05 / 50" N, long. 164° 27 / 15" W. ; depth 36 fathoms ; 

 four specimens. Station 3637, lat, 57° 06' 30" N., long. 170° 28' 00" W. ; 

 depth 32 fathoms; one female with a single young clinging to the an- 

 tennae. 



Arcturus tenuispinis sp. now 



This species is very close to A. cm- untax Beddard. The head is deeply 

 excavated in front ; a pair of spines arise in front of the interocular space 

 and extend forward, diverging a little 

 more than those <>f A. cornutus. The 

 first segment of the antennae extends be- 

 yond the lateral projections of the head 

 not more than 0.2 of a mm. ; the second 

 joint measures about 1.4 mm. on the 

 upper surface, the third joint 5 mm., 

 and the fourth 13 mm. in length ; the 

 fifth joint is lost or broken in both spec- 

 imens. The antennulse reach the mid- 

 dle of the third segment of the antennae. 

 The first and second thoracic segments 

 are both armed with epimeral spines 

 and a pair farther back and higher up 

 on the segment; the other segments of 

 the thorax have epimeral spines only ; 

 the first segment of the abdomen has a 

 pair of spines in line with the epimeral 

 spines of the thorax; the second seg- 

 ment is altogether unarmed; the last 

 segment has two paired spines and one 

 unpaired ; the latter is at the terminus 

 of a dorsal carina which can only he 

 made out with difficulty. The largest 

 spines on the body are the pair at the 

 sides on the proximal end ; the spines at 

 the distal end are slender ; the terminal outline of the segment is rounded. 



A. tenuispinis can be distinguished from cornutus by the more slender 

 spines, by the lack of the extra pair on the third and fourth segments of 

 the thorax, the unarmed second segment of the abdomen, the lack of 



Fig. 7. — Arcturus tenuispinis. (X 2.) 



