ISOPODS OF NORTH AMERICA. 



249 



\ 



the head between thera and a little anterior to them curving down- 

 ward, so that in a dorsal view the anterior margin seems slightly 

 excavate. The eyes are very indistinct, and have almost disappeared; 

 traces of them are seen on the lateral margins, halfway- between the 

 anterior and the posterior margins. The first pair of antenna? are 

 composed of eight articles and extend almost to the posterior margin 

 of the head. The basal articles of the first pair of antenna^ are widely 

 separated by a distance equal to 2 mm. The second antennie are com- 

 posed of nine articles, and extend three articles beyond the first pair 

 of antennte. The maxillipeds have a palp of two articles. The palp 

 of the mandibles is composed of three articles. 



The first segment of the thorax is about one and a half times longer 

 than any of the three following segments, which are subequal. The 

 fifth and sixth segments are 

 each about half as long as 

 any of the three preceding 

 segments in the median dor- 

 sal line. The seventh seg- 

 ment is about Jialf as long- 

 as the sixth. The epimera 

 are distinctly separated on 

 all the segments with the 

 exception of the first; they 

 are narrow, elongate plates, 

 which in the second, third, 

 and fourth segments extend 

 a little more than two-thirds 

 the length of the segment, 

 in the fifth extend almost to 

 the post-lateral angles of the 

 segment, and in the last two 

 extend quite to the extrem- 

 it}' of the post-lateral angles. 



The abdomen is deeply set in the thorax, the post-lateral angles of 

 the seventh thoracic segment reaching to the anterior portion of the 

 sixth abdominal segment. All the segments of the abdomen are dis- 

 tinct. The first is abruptly v^ery narrow; the others gradually increase 

 in width to the last. The terminal segment is twice as wide as long, 

 4i mm. : 9 mm. The post-lateral angles are widely rounded and the 

 posterior margin slightly excavate in the middle. The uropoda are 

 short, extending a little beyond the median transverse line of the 

 terminal abdominal segment. The outer branch is a little longer than 

 the inner branch. Both are similar in shape, and terminate in nar- 

 row, rounded extremities. 



Fig. 260. — Cymotiioa exci.sa. a, Second maxilla, x 39. 

 6, First maxilla, x 39. c, Palp of mandible, x 39. 

 d, Maxiij.iped. X 39. e, Mandible, x 39. /, Seventh 



LEG. X 7. 



