Garman.] 214 [May 2, 



The brown color predominates on the ventral surfaces of the old 

 ones, the white remains in irregular patches near the centre ; the 

 bands which mark the sides of the tails of the young are lost. 



This species is readily distinguished from Humboldtii by the 

 roundness and thinness of the disk and by the tubercles. It differs 

 from motoro in teeth and markings. 



Fourteen specimens from the Thayer Expedition. 



Ellipesurus spinicauda of Schomburgk is probably a mutilated 

 specimen of one of the varieties of this species. The shape and 

 thinness of the body and the coloration favor this conclusion. The 

 length given by the author includes that of the tail ; if this be sub- 

 tracted, the length and width of the disk must be nearly equal. 

 " Like others of the species, they dig holes in the sand, in which 

 they lie flat, and there await their prey." This being the case, it 

 would be difficult to imagine how the creature makes its captures 

 without the spine. 



Under each species of the genus there are one or more varieties. 

 Specimens of the same species from different rivers of the South 

 American system present marked differences. If the river faunse 

 were completely isolated, one could hardly hesitate in pronouncing 

 the distinctions specific. Connected as they are, the intermediate 

 forms are so numerous and the transitions so gradual that the char- 

 acters seized upon in specimens from a particular locality are soon 

 lost without having served for purposes of limitation or definition. 



The possession of such local characteristics in representatives of a 

 species from different rivers, as the Madeira, Tapajos and Araguay, 

 suggests a comparative absence of migration. It may be that the 

 greatest changes of locality are those called for by shrinkage in the 

 water area during the dry season. 



A more comprehensive knowledge of the movements and habits 

 of the fresh water fishes of South America is a matter of the utmost 

 importance to Zoology. The results to be attained by a Brazilian 

 Fish Commission would form a princely gift to science. Possibly we 

 may have these results without the long delay and laborious collation 

 of isolated facts attending the growth of Ichthyology elsewhere. 

 Science has good reason for hope in the friendship of such a ruler as 

 His Majesty, the Imperial Philosopher, Dom Pedro II, Emperor of 

 the Brazils, to whose friendly interest the Museum is greatly in- 

 debted for the collections from which these notes have been taken. 





