192 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 18 



and the posterior edge heavily setose. These setae appear only in large 

 adults. 



Telson. — The shape may be long and slender, with acute apices, 

 or short and stout with rounded apices. The apical armature of each 

 lobe may consist of 3 long setae or 1-2 short spines, with or without 

 a feathered seta. In a few species such as P. miller'i the dorsal proximal 

 armature may consist of stout spines on each lobe, while in the remaining 

 species it consists of 1 or 2 feathered setae. 



Sexual Characters in Paraphoxus 



Unlike most amphipods, sexual dimorphism does not affect the 

 gnathopods; rather it involves the eyes, second antennae and third 

 uropods. Most specimens of the genus which are encountered are 

 females, the ratio running in an order of magnitude of 10:1 or greater. 



Eyes. — The compound eyes of females are small but this smallness 

 may vary in its degree in different species, so that the size may be 

 useful as a systematic character. For instance it is most useful when 

 comparing the very diminutive eyes of P. daboius (Plate 10, fig. A) 

 and the medium sized ones of P. lucubrans (Plate 12, fig. A), two 

 species otherwise similar. 



The eyes of adult males are so large and occupy so much of the 

 breadth of the dorsal surface of the head that it is difficult to see 

 relative differences in size in various species, although drawings often 

 show them. The eyes of young males are scarcely larger than in their 

 females, but the increase to adult size apparently occurs in a few 

 instars. In some way, the large eyes of adult males must be associated 

 with their positive phototropism at night, when they are attracted to 

 a night-light, while females are not (Fage 1932). 



Second antennae. — The flagellum of the second antenna in female 

 paraphoxids is shorter than the peduncle and composed of rather 

 slender, moderately long articles lacking sensory appendages. Young 

 males bear second antennae with flagella slightly longer than the 

 peduncle, the articles being short and stout and much more numerous 

 than in females. It is apparent that at the outset of sexual maturation, 

 flagellar segments undergo rapid proliferation, and increase in length 

 at later instars. Male animals bear second antennae which are as long 

 as or longer than the body and composed of long, slender articles. 

 Some of the proximal articles may have sensory clubs and the distal 

 dorsal side of peduncular article 5 may also have sensory clubs. Articles 

 3 and 4 of the peduncle often have thick tufts of dorsal hairs. 



