ISOPOD8 OF NORTH AMERICA. 



289 



articles. The first antennae extend to the posterior margin of the 



head. The second antennae have the first two articles very short and 



equal in length; the third and fourth are about equal in length and 



each is twice as long as the second; the fifth article is one and a half 



times longer than the fourth. The flagellum is 



composed of nine articles. The second antennae 



extend almost to the posterior margin of the first 



thoracic segment. The maxilliped has a palp of 



five articles. The mandible has a palp of three 



articles. 



The first segment of the thorax is a little longer 

 than- any of the others. The lateral parts of all 

 the segments are bent downward, forming an 

 angle with the dorsal portion. The epimera are 

 not distinct from the segments, but are indicated 

 by a faint line on either side of the segment 

 a little distance within the place where the 

 lateral part of the segment forms the angle with the dorsal part. 



The abdomen is composed of two segments. The first segment has 

 three suture lines on either side, indicating three coalesced segments. 

 The terminal segment is triangular in shape with apex rounded. The 

 uropoda are very large, both branches extending to the tip of the 

 abdomen, and being of equal width. The outer movable branch is 



FIG. 301. EXOSPHAiROMA 

 AMPLICAl'DA (AFTER 



STIMPSON). x 8. 



FIG. 302. EXOSPHAIROMA AMPLICAUDA. a, 6, MANDIBLES. X 51|. C, MAXILLIPED. X 51|. (/.FRONTAL 



LAMINA AND CLYPEl'S. 51}. 



rounded posteriorly. The inner immovable branch has the outer post- 

 lateral angle rounded, the inner one produced. 



The last three segments of the thorax and the first segment of the 

 abdomen have rudiments of tubercles on their posterior margins. 

 In the specimens examined there are no tubercles on the anterior seg- 

 ments, which may be due to size, all the specimens being very small. 

 There are also four tiny tubercles arranged in two longitudinal series 

 of two, one on each side of the median line at the base of the terminal 

 segment. The legs are all ambulatory. 

 2858905 19 



