180 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 18 



9. Head lacks dorsal crest, uropod 2 usually lacks apical ramal 



spines 10 



10. Antenna 2 in male very short Harpinia 



10. Antenna 2 in male as long as body Harpiniopsis 



11. Antenna 2 with basal ensiform process Heterophoxus 



11. Antenna 2 lacks basal ensiform process Proharpinia 



Relationships of Phoxocephalid Genera 



It is possible to determine the structure of a primitive phoxocephalid 

 from an approximate analysis of the conservative features of other 

 gammaridean amphipods and then to hypothesize an approximate tree 

 of successive relationships between the living genera. This tree is 

 diagrammed below. 



None of the existing genera bears all of the features which must 

 be hypothesized for the primitive phoxocephalid: animals with ridged 

 triturating mandibles; eyes; biarticulate palps of the first maxillae; 

 long male second antennae; distally setose fourth article of the 

 maxillipedal palp. 



The basic division between the existing groups seems to be the dif- 

 ference between steno- and eurypodous second articles of the third 

 peraeopods, resulting in harpiniid and paraphoxid stocks. This contrast 

 seems to be more basic than the loss of eyes in certain groups, or 

 the fusion of the two articles of the first maxillary palp in others, 

 as well as other minor characters which might be used. It is interesting 

 that one species assigned now to the genus Phoxocephalus bears a 

 stenopodous third peraeopod. It differs from all other species in the 

 harpiniid stock in the ridged molar processes of the mandible. 



The harpiniid stock has been characterized by a progressive loss 

 of eyes and reduction of the male second antennae. 



The paraphoxid stock has two branches, characterized by the palp 

 of the first maxilla. Phoxocephalus stands at the base of this branch, 

 while Metaphoxus and Leptophoxus have lost the molar ridges of the 

 mandible. The other branch is composed mainly of the genus 

 Paraphoxus, with Microphoxus a primitive limb due to the setosity of 

 the maxillipedal palp article 4. The genus Joubinella is a pelagic genus, 

 similar to Paraphoxus, except for its eusirid gnathopods, typical of other 

 pelagic amphipod genera. 



iA 



