190 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 18 



differentiates it from P. o. obtusidens (Plate 34, fig. H) but in general, 

 species may be differentiated by other criteria. 



The important features of peraeopod 5 are the shape and armature 

 of article 2. The expansive posterior lobe of this article varies in its 

 downward extension to articles 3, 4, or 5. More important than this 

 is the sculpturing of its posterior edge. It may be nearly smooth as in 

 P. obtusidens (Plate 32, fig. Q) with the teeth very shallow and 

 scarcely evident; it may bear 3 to 9, small to large teeth as in most 

 species (Plate 6, fig. R) ; or it may be produced into one or two large 

 spurs as in P. bicuspidatus (Plate 15, fig. P). Little variation in spurs 

 of species such as P. bicuspidatus has been seen but in species such as P. 

 variatus (Plate 3, fig. M and Plate 4, figs. D, M, V) and others 

 bearing small teeth, a variation of one to four in the total number has 

 been observed. Tooth size generally remains stable except in P. variatus, 

 where the extremes are great. 



The sweep point is defined as the point where the posterior and 

 lower margins of article 2 meet. It varies considerably but its usefulness 

 has not been emphasized prior to the present study. 



Uropod 2. — The spinal armature on the peduncle of this appendage 

 varies remarkably from species to species. Two extremes of this are 

 seen in P. heterocuspidatus (Plate 19, fig. V) and P. epistomus (Plate 

 6, fig. T). In the former species the upper edge of the peduncle is 

 armed with very short, stout spines, few in number, whereas in the 

 latter species it is armed with long, slender, numerous setae. These 

 differences can be seen readily in an undissected specimen. 



Other differences in second uropods are minor in nature. 



Third pleonal epimera. — In 1930 K. H. Barnard noted the need 

 for more attention to the configuration and setal armature of the third 

 pleonal epimera in the Phoxocephalidae. Differences between species in 

 most known species are quite minor, variable between sexes and ages, 

 but a few species such as P. robustus (Plate 25, fig. T) and P. pinguis 

 (Plate 44, fig. A) have a large tooth at the lower corner, which 

 distinguishes them from other species having a rounded lower posterior 

 corner. 



The simplest expression of shape occurs in P. oculatus (Plate 28, 

 fig. F) with an unarmed and rounded corner. However, the posterior 

 part of the epimeron is somewhat prolonged, unlike other known 

 paraphoxids. In most species the lower corner bears a small cusp and 

 one or more setae, the posterior edge being slightly convex and not 



