THE DISTRIBUTION OF FRESHWATER CRAYFISHES. 815 



fishes, some very curious points of approximation become 

 manifest. The Sahnonidce, or fishes of the salmon and 

 trout kind, a few of which are exclusively marine, many 

 both marine and freshwater, while others are confined 

 to fresh water, are distributed over the northern hemi- 

 sphere, in a manner which recalls the distribution of 

 the Potamobine crayfishes,* though they do not extend 

 so far to the South in the new world, while thej^ go a 

 little further, namely, as far as Algeria, Northern Asia 

 Minor, and Armenia, in the old world. With the excep- 

 tion of the single genus Reti'opinna, which inhabits New 

 Zealand, no true salmonoid fish occurs south of the 

 equator ; but, as Dr. Giinther has pointed out, two 

 groups of freshwater fishes, the HcqAochitonidce and the 

 GalaxidcBj which stand in somewhat the same relation to 

 the SalmonidiB as the Parastacidce do to the Potamohiidcs, 

 take the place of the Sahnonidce in the fresh waters of 

 New Zealand, Australia, and South America. There 

 are two species of Hajplochiton in Tierra del Fuego ; and 

 of the closely allied genus Prototroctes, one species is 

 found in South Australia, and one in New Zealand ; of 

 the Galaxidce, the same species, Galaxias attennuatus, 

 occurs in the streams of New Zealand, Tasmania, the 

 Falldand Islands, and Peru. 



Thus, these fish avoid South Africa, as the crayfishes 



* According to Dr. Giinther their southern range is similarly limited by 

 the Asiatic Highlands. But they abound in the rivers both of the old 

 and new worlds which flow into the Arctic sea ; and though those on 



