422 PROCEEDINGS OF THE NATIONAL MUSEUM vol. m 



greatest width is seen in the second segment of the metasome, which 

 segment is that of the first swimming legs. The third metasome seg- 

 ment has the posterior lateral margins strongly produced caudad as 

 rounded lobes. The urosome is 5-segmented, with no ornamenta- 

 tion of spinules. The metasome slightly exceeds the urosome in length. 



The rostrum is distinctive in this species. At the anterior limit of 

 the structure, there is great lateral expansion, equivalent to that seen 

 in P. columhiae. There is here, however, no further production of the 

 structure into auxiliary knobs or spines like those seen in the previ- 

 ously described form. 



The antennules are of generalized structure, departing only in in- 

 significant details from the appendage as described and figured above 

 for P. panopeae. In the present species, there is a heavier chitini- 

 zation of the anterior and posterior margins of the more proximal 

 segments. 



The distinction of the antenna from that of the species described 

 above must be principally on subtle variations of the proportions of 

 the component segments. A pronounced proximal constriction of the 

 second segment produces a distinctive club-shaped contour (fig. 37, B) . 



The mouth parts resemble those in the species heretofore described. 

 The most notable feature is the extreme reduction of the maxilliped. 

 It retains the usual three segments (fig. 37, C) , but the size is reduced 

 so greatly that the sum of the lengths of the three segments is less 

 than half the length of the basal segment of the maxilla. The basal 

 segment is expanded and articulates with a complex set of very heav- 

 ily chitinized ridges on the ventral surface of the head. 



The rami of the swimming legs are all 3-segmented. The comple- 

 ment of spines and setae is exactly that presented in detail above for 

 P. columhiae. The ornamentation of the terminal segment of the 

 fourth endopodite is distinctive. The very long medial spine is nearly 

 two and one-half times longer than the lateral spine (fig. 37, D) . The 

 basipodites of the first three pairs of swimming legs bear the usual 

 marginal fringes, but they are composed in this species of exceptionally 

 stout, numerous spinules. The fourth basipodite is fringed by sparsely 

 distributed, short, fine cilia. 



The outline of the fifth leg presents a rounded expansion at the base 

 (fig. 37, E). The terminal outgrowths are relatively short, subequal, 

 the more posterior (medial) stouter and more spinelike. 



The caudal rami are of moderate length (fig. 37, F). The ratio of 

 length to greatest width is about 3.5. The proximal lateral seta is 

 articulated at a point well short of half the length of the ramus. The 

 two elongate, central apical setae are jointed at their bases. The 

 longer of the two is more than three times the length of the ramus. 

 None of the setae of the caudal ramus is ciliated. 



