ISOPODS OF NORTH AMERICA. 503 



Head us wide us lono-, 1^ mm. :1^ mm., with the anterior marg-in 

 sti'aiyht and pi-oduced at the sides in small lateral processes. Poste- 

 rior marg-in rounded. Head deeply set in thorax. Eyes absent. 



The seven segments of the thorax are well defined on one side and 

 in the dorsal region. On the opposite side, however, they merge 

 into and are continuous with the large marsupial pouch which occu- 

 pies the entire ventral and lateral portion of the individual. 



All seven legs are present on the side of the body which has the seg- 

 ments well defined. On the opposite side, however, only the first leg 

 is present. Ovarian bosses are present on the first four segments on 

 the shorter side. Lateral to these are the epimera which occupy the 

 whole of the lateral margin. Epimera are also present on the last 

 three segments on the shorter side. Neither ovarian bosses nor epim- 

 era are present on the longer side of the bodv. 



The abdomen is composed of five segments, all distinct. The fifth 

 segment is very small and tapei's posteriorly to a pointed extremity. 



There are no uropoda. There are four pairs of double-branched 

 pleopoda. The outer branches are large oval, elongated lamella?, leaf- 

 like in shape and larger on the larger side of the bod}", where they lie 

 upon the dorsal surface of the marsupium in its expanded lateral 

 portion. The inner branches are small. There are five pairs of 

 incubator}^ lamelhv, of which those of one side are large and greatly 

 d(iveloped, occupying the whole of the lateral and ventral side of the 

 body and completely inclosing the eggs, while those of the shorter 

 side of the bod}' are very small and much reduced in size. 



The male is narrow, elongate, 8 mm. long and 1 mm. wide. The 

 head is rounded anteriorly and the eyes are present. The first pair 

 of antenna? consist of three articles. The second pair of antennae are 

 composed of four or five articles. 



The seven segments of the thorax are well defined, and have the 

 lateral margins straight. All the segments of the abdomen are coal- 

 esced in a single segment which tapers to a pointed extremity. There 

 are no uropoda or pleopoda. 



The specimen described is found parasitic on Spirontocaris town- 

 sendi Rathbun. 



82. Genus lONE Latreille. 



Female with the lateral parts or pleural lamellae of the abdomen 

 elongated, digitate. 



There are usually tive [)airs of d()uble-])ran(hed pleopoda. The 

 uropoda consist of two elongate simple curved processes, with mar- 

 gins smooth, not digitate. Male with the segments of the abdomen 

 more or less fused; lateral parts or pleural lamella? in the form of 

 narrow elongated processes. 



Branchial parasites. 



