Arcturichi in tin V. S. National Museum. 



45 



basal joints of the median antenna? are oblong and flattened ; the outer 

 antennae are 52 mm. in length ; the first two joints are but little longer 

 than broad, while the three distal joints are long; all are unarmed; the 

 flagellum is composed of about 12 short segments. 



The spines of the head and dorsal region are placed like those of 

 baffini ; with the exception of those on the posterior portion of the thorax, 

 they are much longer than in any specimen of baffini that I have seen ; 

 the spines of the head are 6.5 mm. in length, while those of the second, 

 third, and fourth segments are hut little shorter. The spines on these 

 segments are united at the base by a low ridge which curves up on the 

 spines, giving them the appearance of parts of a single structure. Be- 

 tween the anterior spines and the epimeral projections on their respective 

 segments are low protuberances ; ridges also 

 run from the bases of the spines along the 

 margins to the posterior angle of the segments, 

 leaving a deep transverse groove below the 

 spine. The spines of the first thoracic seg- 

 ment are very small and inconspicuous ; it is 

 possible that this segment may not be normal 

 in regard to the spines, as it is partially over- 

 grown by a colony of Polyzoa. 



The epimera of the second, third, and fourth 

 segments increase in size posteriorly ; they are 

 flattened on the exposed surface and evenly 

 rounded below ; there is a depression on the 

 exposed face. Viewed from above, the epim- 

 eral projections are covered by large rounded 

 tubercles on the lower margins of the seg. 

 ments. The epimera of the fifth, sixth, and 

 seventh segments decrease in size posteriorly, 

 and are broad and wedge-shaped ; the spines 

 of these segments are the same in character as 

 those of the anterior segments, but are much 

 smaller, measuring on the fiftli :! mm., the 

 sixth 2.3 mm., seventh 2 nun. 



The first abdominal segment is very short, 

 with two small spines above and two conical 

 projections below ; the second segment has 

 two long spines above, pointed backward, and 

 none below ; the terminal segment has two 

 spines pointing backward inserted at about the middle of the dorsal sur- 

 face ; at this point the segment is rapidly depressed to the terminal points; 

 the lower margin has two pairs of triangular projections ; A. baffini has 

 but one pair. 



Station 3599, latitude 52° 05' 00" N., longitude 177° 40' 00" W., 55 

 fathoms. Type (No. 20530, U. S. X. M.)'- 



Fig. 4.- 



-Arcturus longispinis. 

 (X ltf.) 



