GAMMARIDEAN AMPHIPODA 21 



identify specifically because most of the conspicuous taxonomic 

 characters are found on male second gnathopods. Terminal adult 

 males of Photis spp. are, perhaps, rarer than those of any other 

 sexually dimorphic group collected in this survey. Ovigerous females 

 and young males obviously are sufficiently common to sustain inter- 

 tidal populations but subterminal males are remarkably similar among 

 the several species. If the autecologist were to require identification of 

 young individuals, a morphometric analysis of various character 

 proportions would be needed. The large background-count of juvenile 

 photises in these samples has complicated the recognition of allied 

 genera having small-bodied adults. The distinctive third uropod of 

 photises can be observed readily by placing the specimens on a de- 

 pression slide and utilizing medium powers of compound microscopes. 

 After considerable trial and error the indescribably subtle differences 

 in body shapes of juvenile photids can be recognized and the individual 

 mounting dispensed with. Juvenile photises especially may be con- 

 fused with adults of Microjassa litotes. Specimens of the latter species 

 are distinguished by their shiny bodies and pale pink eyes (in alcohol) . 

 Juvenile photises have dull bodies and darkly pigmented eyes; how- 

 ever, photids preserved for more than a year may lose all pigmentation. 

 Uropod 3 of M. litotes is fully biramous in contrast to those of photises 

 but this condition is difficult to resolve by use of low power dissecting 

 microscopes. 



Photis elephantis, with its elephantine pereopods on terminal 

 males, is a most unusual appearing species. The pereopods autoto- 

 mize readily in preservative. Expanded pereopods apparently do not 

 occur on all terminal males possibly because intersexual development 

 occurs. That the species is not a localized race at Corona del Mar or 

 a diseased population of some other species, are facts suggested by 

 its occurrence in a slightly different morph at the Galapagos Islands 

 (material in hand). 



Although the genus Maera is well diversified in California (5 species) 

 the frequency of individuals is very low in the intertidal. On the other 

 hand, the closest generic relative, Elasmopus, is represented in Cali- 

 fornia by 4 or 5 species, the individuals of which are extremely abun- 

 dant. Both genera are primarily tropical in occurrence. Another 

 genus of Gammaridae, the cold-temperate Melita (3 species in Cali- 

 fornia) is poorly represented in the southern half of California. 

 Individuals of the two northern species are scarce. One of the few 

 tropical melitids, M. appendiculata, is also rare in the Calif ornian 

 intertidal. The latter species is remarkable because of its disym- 

 metrical, ?7ca-like male second gnathopods (see Chevreux and Fage, 

 1925). 



