SOUTH AMERICAN FISHES 



29 



collected by Mr. Heiin, in Ecuador, a few are found which liave 

 the adipose, i. e., these few specimens are still Piabucinas, whihi 

 their brothers and sisters are Libiasinas. It may be well to i)im\i 

 out that Libiasina, until very recently, has been known only from 

 the Pacific slope, Piabucina being its Atlantic slope counterpart. 

 In northwestern Colombia the genera intercross. 



I expect to deal more fully with these and other lines and 

 methods of evolution in the final volume on the Characins, and 

 hope that I can then go into the reasons as well as into the lines 

 and methods. 



B. The Rhoadsin^. 



The Rhoadsinas have been discovered but recently. At present 

 there are two genera and three species known from Transandean 

 Ecuador, Colombia, and Panama. They undergo a remarkable 

 modification with age. The fnll}^ grown adults differ from some 

 of the Tetragonopterina) in having the sides of the lower jaw 

 pressed inward somewhat, raised and provided with thorn-like 

 teeth. The mouth in the adult is very large, there are teeth along 

 the entire edge of the prolonged maxillary, and there is an an- 

 terior series consisting of one or two teeth on the premaxillary. 

 In the young the mouth is minute, the maxillary short, just reach- 

 ing the eye, with one or two teeth. In brief, the young of this 

 subfamily have the characters of the genus Cheirodon, a genus 

 of minute fishes. The subfamily characters become prominent 

 only after the individuals have grown beyond the size of the mem- 

 bers of the genus Cheirodon. 



C. The Iguanodectin^e 



The Iguanodectinae consist of a few species only. They are 

 found from the Essequibo to Paraguay. 



The}^ differ from the Tetragonopterinee in having the gill-nKMri- 

 branes united, free from the isthmus. They are elongate, slender 

 fishes. The mouth is minute ; the teeth are broad, multicuspid 

 incisors. The front row of the teeth has nearly reached the van- 

 ishing point, being reduced to a single tooth in some species and 

 having disappeared altogether in one. In the genus Piabucus, 

 the breast is trenchant and the pectorals are enlarged. I have 

 been inclined to place considerable taxonomic value on this char- 

 acter in the past, but I am sure now that it has several times ap- 

 peared independently in diff'erent groups of tlie Characins. 



