NO. 2165. NEW PARASITIC ISOPOD CRUSTACEANS— HAY. 573 



bosses, those of the last three segments occupying the entire lateral 

 margins. Abdominal segments distinct and with the epimera pro- 

 duced into broad plates which are expanded at the outer end and, 

 with the exception of the first, have their anterior angle drawn out 

 into a more or less prominent tooth- The pleopods are five pairs of 

 elongate, tapering, leaf -shaped, biramous appendages having the 

 margins produced into a number of thick, finger-like processes, which 

 stand at right angles to the plane of the appendage both above and 

 below, giving it the appearance, when viewed from the edge, of being 

 pinnately branched; there may be eight or nine of these processes 

 on each margin of both endopodite and exopodite, but those of the 

 latter branch are reduced in size. The uropods are uniramous and 

 resemble the endopodite of the pleopods. The incubatory pouch is 

 formed by five broad, foUaceous plates overlapping in the middle 

 line; the last four of these plates are approximately alike but the 

 first is divided into two lobes, an anterior and a posterior, by a broad 

 fold; the posterior lobe helps to cover the eggs, the anterior lobe 

 covers the mouthparts and the fold, the margin of which bears 

 processes similar to those on the pleopods, forms the front boundary 

 of the egg chamber. MaxHlipeds broad, roughly quadrangular and 

 divided obliquely into two parts; the anterior inner angle produced 

 into an unsegmented tip; posterior outer angle curved and pointed. 



Male (para type). — ^Much smaller than the female, symmetrical, 

 about three times as long as broad, with aU the segments of the body 

 developed and distinct. There is a pair of very small eyes. The 

 antennules, of three articles, are hidden beneath the margin of the 

 head. The antennae, of four articles, are partly visible from above. 

 The legs are aU ahke and prehensile. The lateral portions of aU the 

 segments of the body are narrowed, the lateral angles tending to be 

 acummate in the thoracic and rounded in the abdominal regions. 

 The terminal segment of the abdomen is reduced to a knobhke 

 structure, nan'ow anteriorly and notched horizontally and vertically 

 behind. 



Six specimens of this isopod, three males and three females, were 

 obtained from the gill chambers of Upogehia affinis. It resembles 

 most closely, perhaps, P. furcata Richardson, but differs from it and 

 aU other American species of the genus in the structure of the pleo- 

 pods of the female. 



