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marbled pattern, although it is somewhat faded from long tenn preservation in 

 alcohol. The smallest specimens of brevifilis examined generally show little trace of 

 marbling and resemble larger specimens in coloration. However, a few specimens 

 of brevifilis (ANSP 39343 [holotype oiA. ogilviei], FMNH 58136, and USNM 

 247251) have an unusual, somewhat intermediate coloration pattern consisting of 

 small, irregular spots and blotches on the dorsum, and, particularly, on the sides in 

 the form of one midlateral row and a shorter sublateral row above the paired fins. 

 These specimens, as well as the majority of other brevifilis material examined, also 

 have strongly mottled paired fins and a large ovoid spot in the adipose fin, similar to 

 marmoratus. Moreover, brevifilis is viddely distributed and occurs at the few 

 localities where marmoratus has been collected; one record from Argentina is based 

 on the description oiA. barranquerensis, the holotype (presumably deposited at 

 MACN) of which was not examined in this study. Ageneiosus barranquerensis, 

 however, is tentatively placed in the synonymy oi marmoratus on the basis of 

 illustrations accompanying the original description (Risso and Risso 1964:plate 2), 

 which clearly show the strong mottling pattern found in no other species. Because 

 the amount of material oi marmoratus and small specimens oi brevifilis currently 

 deposited in museum collections is inadequate to elucidate possible ontogenetic 

 changes in coloration, I choose to recognize these two taxa as distinct species ' 

 pending further studies. The solution to this problem will require collections of 

 complete growth series, similar to the study by Lundberg et al. (1989), in which it 

 was shown that the large pimelodid Sorubimichthys planiceps undergoes pronounced 

 coloration changes during development. 



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