CHAPTER IV. 



THE GEOGRAPHICAL DISTRIBUTION OF THE FRESHWATER FISHES OF 



BRITISH GUIANA. 



Every effort was made to secure a complete series of the fishes of the area 

 covered, and reasonable success may be claimed, the ichthyic fauna at large being 

 well represented by the eighteen thousand three hundred odd specimens collected. 



Inasmuch as several localities were examined in each of the following districts, 

 (1) the lowlands, (2) the middle Essequibo, (3) the lower Potaro, (4) the upper 

 Potaro, we may also conclude that the faunas of these stretches of territory are well 

 illustrated by the material collected. Furthermore, the work on such units of 

 environment as the trench in the Botanic Garden, the woodland creek and sand- 

 bank at Rockstone, the Konawaruk pool, and the Amatuk Cataract was entirely 

 satisfactory. 



On the other hand, it may be doubted whether the lists of specific localities 

 are in many other cases exhaustively complete. I have called attention to this 

 matter in connection with the species taken at Rockstone and nowhere else. It was 

 found that many of these are known to have a wide distribution and must occur 

 in other localities in the area under consideration, although they were not taken 

 elsewhere. 



Furthermore, it must be regretted that time did not permit me to make a 

 more exhaustive study of the fauna in the Potaro between Amatuk and Tukeit 

 and" above the Kaieteur. 



General Plans for Distributional Work. 



A question of greater interest to the next expedition than to the general account 

 of the present trip is the length of time that should, and could to advantage, be given 

 to any one place, and how far apart stations should be selected. To graphically 

 demonstrate conclusions I have prepared two tables. - 



On p. 84 is a summary showing the total number of species taken at each place, 

 and on p. 85 a summary of the number of species taken at but one locality. The 

 latter shows how much would have been lost from the total number of species, had 

 any particular locality been skipped. Only Kangaruma yielded nothing new, and 

 fishing here was but a minor incident. There is very great inequality. The omis- 

 sion of Konawaruk, where two hours were spent, would have entailed nearly as 



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