ISOPODS OF NORTH AMERICA. 



597 



the l)asal article .short; the second is al)ont twice as long as the rirst; 

 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 

 llagellum is composed of three sul)e(iual articles. The antennae 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 PERCONVExrs. a, Maxilliped. x20i. 6, Second antenna 



MAXILLA (inner LOBE). X39. cl, SECOND MAXILLA. X20^ 



x20|. /, Mandible. x20i. g. First antenna. x39. 



xllj. c, First 

 First maxilla (outer lobe). 



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 1\ 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 nun. wide at 

 the base and 1^ mm. long. The uropoda extend 1 mm. bej'ond the 

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

 abdomen. The inner ])ranch extends only to the middle of the outer 

 branch and is more slender. 

 All the legs are ambulatorv and covered with stiff hairs. 



Fig. 654.— Alloniscus per- 

 coNVEXus. Terminal 

 segment of abdomen 



WITH UROPODA. Xlli. 



