240 TJniversitij of California PnhJications in Zoology. [Vol.4 



above, darker toward the apex of the dorsal segments and on the 

 head. It is thus easy to distinguish the two species by their 

 appearance, although the coloration is not entirely constant. 



Antennae. — The spiny armature of the antennae in the dif- 

 ferent stages varies surprisingly, and might readily prove the 

 source of no little confusion. As a rule in the young and in the 

 females the two pairs of antennae are much more nearly equal in 

 length than in the grown males (compare fig. 39 with fig. 38). 



Even very minute females show distinctly a developing egg 

 sac, and very small individuals, with by no means fully developed 

 antennae, sometimes bear egg-masses. I have found females of 

 salmonis in several stages, as also of spinicorne, and fully devel- 

 oped males of salmonis, but of spiidcorne only stages that possibly 

 do not represent the maximum development of the male. In 

 salmonis the second antennae of the males, at least of those fully 

 grown, are very much longer and stouter than those of the female 

 (pi. 13, figs. 38, 39). This is not so noticeably the case in males 

 of spinicorne, but may prove to be so if more fully developed 

 males are found (pi. 13, figs. 36, 37). 



First Maxillae.— (PI. 9. fig. 9; pi. 11. fig. 25.) The apical 

 teeth of the palp of the first maxillae of salmonis are seven in 

 number and do not form a complete circle; in spinicorne they 

 form a complete circle and are about twelve in number, one of 

 the outer ones serrate : on the ramus about three of the teeth are 

 bifid in salmojiis. 



Peraeopods.— (PI. 10. figs. 14, 17; pi. 12, figs. 31. 34.) The 

 basal segment of the fourth peraeopod is broader in salmonis, and 

 the second row of styles on the carpus terminates in two long- 

 straight spines. 



Uropods.— (PI. 10, fig. 19; pi. 12. fig. 35.) The first and 

 second uropods show a stout tooth-like process on the apex of the 

 first segmeiit in salmonis; both rami of the first uropod have 

 about eight spines, longer and stouter than those of spinicorne, 

 especially than the dozen or so on the outer ranuis; the outer 

 ramus of the second uropods has in salmonis three long apical 

 styles, and the inner ramus bears about two apical styles and the 

 two large ones along the margin ; the basal segment of the third 



