ISOPODS OF NORTH AMERICA. 



597 



the basal article short; the second is about twice as long as the first; 

 the third and fourth are subequal and each is a little longer than the 

 second; the fifth is one and a half times as long as the fourth. The 

 flagellum is composed of three subequal articles. The antennas are 

 covered with small spines. The maxillipeds have a palp of three arti- 

 cles. The palp of the mandibles is wanting. 



d e f g 



FIG. 653. ALLONISCUS PERCONVEXUS. a, MAXILLIPED. x20. 6, SECOND ANTENNA. xlH. c, FIRST 

 MAXILLA (INNER LOBE). x39. d, SECOND MAXILLA. x20J. e, FIRST MAXILLA (-OUTER LOBE). 

 x2<H. /, MANDIBLE. x20|. g, FIRST ANTENNA. x39. 



The first segment of the thorax is 2 mm. in length and is a little longer 

 than any of the others, which are subequal and each is about li mm. 

 long. The lateral margins of all the segments are 

 straight and contiguous. On the first four seg- 

 ments the epimera are indicated by a distinct lon- 

 gitudinal suture, which on the first segment is con- 

 fined to the posterior half of the segment, but in 

 the three following segments extends the entire 

 length of the segment. There are no suture lines 

 on the last three segments. 



The abdomen is as wide as the thorax. The 

 first two segments have the lateral parts covered 

 by the seventh thoracic segment. The sixth or terminal segment is 

 triangular in shape and is twice as wide as long, being 3 mm. wide at 

 the base and 1| mm. long. The uropoda extend 1 mm. beyond the 

 extremity of the abdomen. The peduncle does not extend beyond the 

 abdomen. The inner branch extends only to the middle of the outer 

 branch and is more slender. 

 All the legs are ambulatory and covered with stiff hairs. 



FIG. 654. ALLONISCUS PER- 

 CONVEXUS. TERMINAL 

 SEGMENT OF ABDOMEN 



WITH UROPODA. Xlli. 



