SOME BRACKISH-WATER AMPHIPODA. 663 



peduncle is noticeably shorter than that of ant. 2, extending only 

 to the distal end of the 4th joint of the latter, instead of to half 

 the length of the 5th, as in our species; both the peduncle and 

 flagella are very sparsely provided with setse, and the accessory 

 llagellum is much longer, 13-14-jointed in the male, with about 

 47 joints in the primary. 



Antenna 2 shorter ; 4th joint of the peduncle slightly shorter 

 than the 5th, both furnished inferiorly with the characteristic 

 clusters of setae. The flagellum is about as long as the 4th and 

 5th joints of the peduncle combined, 11-jointed in the largest 

 Bremerhaven specimen, 15-19-jointed in the large males from 

 Rauschen ; in both sexes calceolse occur on the proximal joints 

 and clusters of sette similar to those of the peduncle. 



In the male of G. locusta, and to a less degree in the female 

 also, both the peduncle and flagellum are clothed with dense tufts 

 of long fine delicate setfe. The almost glabrous first antenna 

 and the exceedingly hairy second antenna of G. locicsta are suffi- 

 cient to distinguish the species from G. zaddachi at a glance. 



Gnathopoda. — The difference between the gnathopods of the 

 males of the two species will be better seen by referring to 

 PI. LXXIII. figs. 2-5. In G. zaddachi (fig. 2) they are much 

 broader in proportion to their length, with the palm less oblique 

 and the palmar margin crenulate. In G. locusta (fig. 3) the 

 palmar margin is sinuous, the clusters of setae on the hind margin 

 are much denser, the setae, as in ant. 2, are very fine and long, 

 and the palmar spines are of different structure. 



In the female (figs. 4 & 5) the second gnathopod only carries a 

 spine midway on the palm ; the finger is much more pointed than 

 in the male. 



Permo-poda. — The proportions differ from G. locusta, the 4th 

 joint being much shorter in proportion and broader, and the 6th 

 joint, except in perseopod 1, always exceeds it in length. The 

 2nd joint in peraeopod 3 has the lower hind corner produced, sub- 

 acute ; this joint in peraeopods 4 and 5 is narrowed distally, the 

 hind corners not free, but with one or two strong spines inset at 

 the angle (see fig. 10). In most of the large males the basal joints 

 are long, very narrow, and scarcely at all expanded posteriorly; in 

 the female and immature specimens they are always shorter and 

 more expanded than in the adult male. Generally speaking the 

 posterior margins of the basal joints and the inferior margins of 

 the 2nd and 3rd pleon segments are beset with small spines in 

 the brackish-water form, and with long setiform spines or sette 

 in the freshwater form, but this again is not an invariable rule, 

 some specimens having spines on the hinder peraeopods and setae 

 on the pleon epimera or vice versa. The hinder peraeopods in the 

 freshwater animals are covered with long fine hairs set in clusters 

 with the spines ; these hairs are not much developed in the animals 

 from salt water, but, on the other hand, they are provided with 

 more spines. 



The uropoda are more slender than in G. locusta. In uropod 3 



