On the Fish-fauna of the Rio de la Plata. 7 



II. — A Contribution to the Knowledge of the Fish-fauna of 

 the Rio de la Plata. By Dr. A. Gunther, F.R.S., Keeper 

 of the Zoological Department, British Museum. 



[Plate II.] 



The Fish-fauna of the Rio de la Plata and of the large 

 affluents which discharge their waters into that estuary is 

 but little known. On preparing a list of the species described 

 by ichthyologists as occurring in the various parts of this 

 great river-system, I found their number to amount to 153. 

 But so little is known as regards the distribution of the species 

 within the main river and its tributaries that that list utterly 

 failed to fulfil the purposes for which it was drawn up, viz. to 

 elucidate the degree of affinity between the Uruguay, Parana, 

 Paraguay, and the rivers draining the country east of the 

 Cordilleras, and to demonstrate a transition of the fauna of 

 the lower parts into that of the upper — which latter may be 

 supposed to be very similar to that of the San Francisco, 

 so fully described by Dr. Liitken. Therefore it would have 

 been premature to publish such a list, and I propose to 

 limit the present communication to some notes and descrip- 

 tions drawn up during an examination of a considerable col 

 lection of fishes received by the British Museum from Mr. E. 

 White of Buenos Ay res. As a part of these species are 

 identical with those received from the ' Challenger ' expe- 

 dition, I have thought it useful to supplement these notes 

 by adding the names of the fishes obtained from the latter 

 source, full descriptions being given in my " Report on the 

 Shore-fishes " procured during that voyage ; they are marked 

 in the following notes by the letters Ch. The majority of 

 the fishes enumerated in this paper belong to the fauna of the 

 Rio de la Plata proper and of the lowermost portion of the 

 Parana. 



ClIONDKOPTERYGIANS. 



1. Mustelus vulgaris , M. & II. 



2. Raja platana } Gthr. [Ch.] 



3. Raja microps, Gthr. [Ch.] 



4. Trygon hystrix, M. & H. 



I believe that authors have confounded several species 

 under this name. The true Trygon hystrix of the Rio de la 

 Plata has a large eye, the longitudinal diameter of Avhich is 

 two thirds of the width of the cartilaginous space between 

 the eyes ; the spiracles are very large, three times the size of 

 the eye ; and the tail is considerably longer than the body, 



