ISOFODS OF NORTH AMERICA. 61 



short, being- only a.s lono- a.s the lirst abdominal ,seo-nient, and narrower, 

 about one-third as wide as the sixth thoracic segment; it could easily 

 be taken for one of the abdomitial segments. 



The lirst live seg-ments of the abdomen are short, distinct, and sub- 

 equal in length; they are l)ut little wider than the seventh thoracic 

 segment, but abruptly narrower than the sixlh thoracic segment. 

 The sixth or terminal segment is triaugular in shape, with a])ex very 

 acute. The uropoda extend to tln^ extremity of the abdomen. The 

 inner ])ranch is a little wider and a very littl(> longer than the outer 

 branch. Both are narrow, elongate, with extremities obliquely trun- 

 cate, the post-lateral angles being rounded. 



There are apparently only five paii-s of thoracic legs. The first 

 pair are modified and opercular, and are composed of only two arti- 

 cles. The seventh pair are wanting. The remaining live pairs are 

 ambulatory. 



Deaci-lption of female. — Bod}" ovate, about twice as long as wide, 

 2 mm. :4 mm. Head smaller than in male, with the front produced in 

 a lobe which is emarginate in the middle. Eyes 

 small, round, composite, and situated at the 

 post-lateral angles of the head. Antennte of 

 both pairs as in male. 



The tirst segment of the thorax is short and 

 narrow and almost inconspicuous, appearing as 

 a small lobe back of the head. The thorax 

 becomes wider with the second thoracic seg- 

 ment. The second and third segments are short 

 and about equal in length. The fourth and 

 fifth are verv long, many times longer than the '^'^ ^o.-gnathia cerina 



- "' "^ " . , (After Harger). Female. 



preceding segments and scarcely to be distin- 

 guished, being somewhat fused dorsally. They are nearly su})equal. 

 The sixth segment is about half as long as the preceding segment, and 

 becomes gradually narrower from the anterior to the posterior extrem- 

 ity. This segment is also som(nvhat fused dorsally with the preceding- 

 segment. The seventh segment is ver}^ short and narrow and not to 

 be distinguished from the abdominal segments, being of the same length 

 as the five anterior abdominal seginents, but narrower. 



The abdomen is similar to that in the male. The tive posterior 

 pairs of walking legs are similar to those in the male. The first pair of 

 legs are composed of three articles and terminate in a minute rounded 

 lobe. There is a delicate mcinbi-aneous plate attached to the base of 

 the first pair of legs. 



The eggs are very clearly seen in the cavity of the thorax, which 

 they almost completely till. 



Body of female smooth throughout its entire length. 



