FRESHWATER CRUSTACEA OF TASMANIA. 77 



which clearly belong to this genus, and he has suggested that Niphargus mortoni 

 described by Thomson also belongs to Gammarus. 



The two species described below, G. ripensis and antipodeus, are evidently closely 

 allied to Thomson's N. mortoni, and a careful examination of their characters has shown 

 that they are exactly intermediate in structure between the genera Neoniphargus and 

 Gammarus. 



Thus the telson (PI. 14. figs. 19 & 25) cleft to the base and the form of the gnathopods 

 (PI. 14. figs. 20 & 26) are Ganiinarid, while the three-jointed secondary appendage of 

 the 1st antennas (PL 14. figs. 17 & 23), the inner ramus of uropod 3 (PI. 14. fig. 18), the 

 condition of the inner plate of the maxilla (PL 14. fig. 22) are very close to Neoniphargus, 

 but with distinct Gammarid tendencies. With regard to the first maxilla especially, it 

 is to be noted that of G. antipodeus (PL 14. fig. 22) is exactly intermediate between that 

 of Neoniphargus (PL 13. fig. 5) and Ganimarus (PL 14. tig. 27). It is, in fact, very 

 difficult to say to which genus they are more nearly allied, and it would perhaps be 

 permissible to erect a new genus to receive these three species. The occurrence of these 

 intermediate forms between Gammarus and Neoniphargus certainly suggests that Neo- 

 niphargus has been derived independently from Gammarus in the Southern Hemisphere 

 and that it is not genetically related to the Niphargus of the Northern Hemisphere. In 

 this case, the species described by Sayce as Niphargus pulchellus from Victoria (Proc. 

 Roy. Soc. Victoria, 1899, vol. xii.) should not be placed in Niphargus, with which, indeed, 

 it does not closely agree, but in a separate genus. The resemblance of this species and 

 of the numerous species of Neoniphargus to the European Niphargus must then be looked 

 upon as a remarkable case of convergence. 



Gammarus mortoni. 



Niphargus mortoni, Thomson, Proc. Roy. Soc. Tasmania, 1892 (1893), p. 68. 



This species is evidently closely related to the two described below, but probably not 

 identical with either. Thomson's figures do not give quite the requisite details. The 

 form of the telson is, however, different to that in the two following species. 



Occurrence. In a small stream above Pranklin on the Huon River and on 

 Mt. Wellington. 



Gammarus ripensis, sp. n. 



The coxal plates of the fourth pair are normally quadrate in shape. The eyes are 

 oval. 



The first antennas have the peduncle of three subequal joints, clothed with a continuous 

 row of fairly long setae. The secondary appendage consists of three joints (PL 14. 

 fig. 23). 



The gnathopods have the two penultimate joints normal in shape, longer than broad, 

 with the inner surface provided with rows of stout bristles (PL 14. fig. 20). 



The pereiopods are armed with fairly numerous and long setae ; the terminal joint 

 with its claw is slender and rather elongated. 



The third pair of uropods projects distinctly behind the outer two pairs. 



SECOND SERIES. — ZOOLOGY, VOL. XI. 11 



