ISOPODS OF NORTH AMERK^A. 



365 



Body ol)long, ovato, almost three times longer than wide, 7 mm. : 20 

 nmi.; length of abdomen a little more than one-third that of entire 

 body, 8 nun. : 20 mm. 



Head wider than long, slightly exeavate in front. Eyes large, 

 round, compound in strueture, and situated just anterior to the median 

 transverse line on the anterior portion of the head, at the extreme 

 lateral margin. First pair of antennjt? with the basal article not 

 expanded, and equal in length to the second article; third and fourth 

 articles slightly longer than either of the preceding ones. First antennas 

 extend to the end of the third peduncular article of the second pair of 

 antennie. The basal article 

 of the second antennte is 

 short; the second and third 

 articles are about equal in 

 length; the fourth is very 

 little longer than the third; 

 the tifth is about twice as 

 long as the third. The lla- 

 gellum consists of fourteen 

 articles. When retracted, 

 the second antenna^ extend 

 to the middle of the third 

 thoracic segment. Th(> 

 maxillip(>ds have a palp of 

 four articles. 



The segments of the 

 thorax are about equal in 

 length, with the exception 

 of the first, which is some 

 what shorter than any of 

 the others. Theepimeraof 

 all the segments occupy the 

 entire lateral margins of the segments. They are in the form of large, 

 broad plates, gradually increasing in width from the first to the sixth. 



The legs are more or less alike in structure, and have a few hairs on 

 the inferior margins. 



The abdomen has two short segments followed by a long terminal 

 one with sutures at the base. The sides of the abdomen converge to a 

 nai-iow extremity, the width of which is to the base of the abdomen as 

 2:5. The posterior margin of the terminal segment is produced in the 

 middle in an acute })oint, extending some distance beyond the lateral 

 angles. Color varies greatly, being sometimes unifornd}- light or 

 dark green, or brown and often striped with a median longitudinal 

 stripe of a light color and a marginal stripe on (Mther sid(\ or with 

 only marginal stripes. The colors are occasionally ari'angcd in trans- 

 verse bands or blotches. 



Fig. 395.— Idothea baltica. a Maxilliped. x 41. 

 b First antenna, x '23. 



