SOME BilACKISH-WATER AMPHIPODA. 661 



" Lough Awadcly and Tullynabour." 4 specimens, three males 

 and one female, largest 14-15 mm. Freshwater form. 



" Lough Erne." 4 specimens ; two G. zaddachi, male and female, 

 freshwater form ; and two 0. pulex. 



The first to observe the species now under discu.ssion was 

 Zaddach, after whom I have accordingly named it. 



In 1844 he described it under the name of " Gammarus locusta 

 Fabr. ?," but pointed out the characters in which it differed from 

 Milne-Edwards's description, adding that if the latter were cori-ect, 

 his (Zaddach's) species must be regarded as new. In his later 

 work he gives a more detailed description and figures of the species, 

 again, however, emphasizing the difl^erences in the antennae and 

 the 3rd uropods. Zaddach's specimens are still preserved at 

 Konigsberg Museum. The G. locusta, described by Chevreux 

 (Bull. Soc. Zool. V. svii. p. 141) as inhabiting the Loire and 

 the mouths of rivers of Corsica and Provence, is very probably 

 the species here described. 



The principal points of difference between this newly-established 

 species and G. locusta lie in the antennae, in the proportions of the 

 peduncle-joints of antenna 1, and in the setse, in the gnathopoda, 

 in the 4th side-plate, in the armatui'e of the pleon. and in the 

 3rd uropod. 



It difiers from G. duebenii, specimens of which were kindly 

 sent to me by Professor Sars for comparison, in the following 

 points : — -The upper antenna of G. duebenii is only sparsely fur- 

 nished with hairs, and has none of the regular graduated clusters 

 so characteristic of G. zaddachi ; the hands of gnatlis. 1 and 2 are 

 smaller, and practically subequal in size, in G. zaddachi the hand 

 of gnath. 2 is decidedly larger than that of gnath. 1 ; in the adult 

 G. duebenii the basal joints of j^erseopods 3, 4, and 5 are all 

 expanded, with the hind corners free, while in G. zaddachi these 

 joints are hardly expanded at all in the male, and only the 3rd 

 has the hind corner free ; in the largest G. duebenii the 1st and 

 2nd uropods and the telson reach to the level of the peduncle of 

 uropod 3, and the outer ramus of urop. 3 is twice the length of 

 the outer ramus of urop. 1 (in the smaller S|)ecimens the propor- 

 tions are as figured by Sars, Crust. Norway, vol. i. pi. 177); in 

 G. zaddachi urop. 1 is considerably longer than urop. 2, and the 

 outer ramus of urop. 3 only half as long again as that of urop. 1 ; 

 the telson in G. duebenii is shorter, broader, and more spinose. 



From G. pulex it is distinguished at once by the shape of the 

 eye, small and rounded in G. pidex, large and reniform in 

 G. zaddachi ; the antennae, gnathopods, 4th sideplate, pleon 

 armature, and the 3rd uropods also differ. 



The Bremerhaven and Frisches Haff specimens ai'e all young, 

 the largest, a female figured on PL LXXIIL, measuring 9 mm. 

 The largest male in the Konigsberg collection measures 18"5 mm. ; 

 the females are much smaller and broader, 12-13 mm., but none 



