XV. THE SERRASALMINvE AND MYLIN^.i 



By C. H. Eigenmann. 



(Plates XLIV-LVIII.) 



The Serrasalminae and the Mylinae are highl>' specialized fresh- 

 water fishes. They are members of the family of the Characidae, 

 ubiquitous in South America, being rather closely allied to 

 the Tetragonopterinae and the Bryconinae. They are compressed, 

 deep fishes, with a series of median spines along a greater or less 

 part of the ventral surface. The dorsal fin is longer than in most 

 of the other South American characins, and reaches its maximum 

 length in Myleus pacu, which has twenty-seven dorsal rays. The 

 anal fin is long and its base is usually inclined far from the hori- 

 zontal. The predorsal line is naked. The adipose fin is well-devel- 

 oped, and in Piaractiis of the Mylinae and in Pygocentrus of the Ser- 

 rasalminse it is rayed. The mouth and teeth in all cases are highly 

 differentiated and specialized. The number of teeth for the various 

 species is fixed, or in some cases varies one or two teeth on each 

 side of each jaw. 



The teeth in fishe^ ar^ usually small, conical, and arranged in 

 bands. Compara iw fishes have the teeth restricted in number 



and with individ ^aracteristics. In the Mylinae and the Serra- 



salminse the teeth ' few in number and for the most part so special- 

 ized, that it would be possible, in some cases at least, to determine 

 the location in the jaw of any individual tooth. But the dentition 

 in related species, tooth for tooth, is often so similar that it is prac- 

 tically impossible to determine from which of several related species 

 it may have come. The form of the teeth in different genera 

 varies from molar», as in some species of Mylinae, to incisors, 

 which may be bicuspid, tricuspid, or multicuspid. The Serrasal- 

 minae contain a single series of teeth in each jaw and sometimes 

 a series on the palatines. The palatine teeth vary much more in 

 number than the teeth of the jaws. The teeth in Pygopristis denticii- 

 latus of the Serrasalminae are nearly bilaterally symmetric, with 



1 Contribution from the Zoological Laboratory of Indiana University, No. 142. 



226 



