SOUTH AMERICAN FTSTTES 23 



To go beyond the Tetragonopterinae : 



A pair of conical teeth has appeared behind the front series 

 independently several times. 



The pectorals have become enlarged and the pectoral muscles 

 have become enlarged, and a. greater or less trenchant I'idgc along 

 the breast has developed independently several times. 



This independent origin of characters is responsible for the fact 

 that some of the accepted genera of the Tetragonopterinae are of 

 polyphyletic origin, i. e. our definitions of genera are in many 

 cases enumerations of characters frequently independently ac- 

 quired, not enumerations of the characters of the ancestral type of 

 the genus from which the species have diverged. A result of this 

 independent divergence is that frequently in a restricted, isolated 

 area the species of different genera represented in the area are more 

 nearly related to each other than to members of their own genera 

 in remote regions. For instance Astyanax festce and Bryconameri- 

 ctis peruanus of the Pacific slope of Ecuador are more intimately 

 related than festm is to Astyanax anterior of the upper Amazon. 

 And in this case, Astyanax hYevirostris or Bryconamericm hrev- 

 irostris whichever it may be, is intermediate between the two. I 

 am not competent to say whether hrevirostris is moving from 

 Bryconamericiis to become an Astyanax, or whether it has just 

 completed the reverse process. Certainly festce and hrevirostris 

 are more intimately related, have had a common ancestor at a less 

 remote time, than either of them with an Astyanax or Bryconamer- 

 icim of southeastern Brazil. 



We recognize two types of genera, one a group of closely re- 

 lated species, descended from a common ancestor and having 

 certain distinguishing characters in common. Phenacogaster is 

 such a genus. The peculiar scaling of the ventral surface has been 

 developed but once; and the species are all closely allied, differing 

 from eaeh other in but a few characters. The other, a polyphy- 

 letic type, consists of species having a certain combination of 

 definite characters in common which easily distinguish members 

 of the genus, but which, instead of indicating a single ancestral 

 line from which the species have diverged, are acquired possibly 

 one at a time along distinct lines converging to a common defini- 

 tion.^ Sometimes the polyphyletic origin can be detected, some- 

 times not. Bryconamericus seems to me to be such a genus; 



iln traveling in the tropical forest, two plants that pleased the eye more than any others are the 

 glorious, independent, self-sufficient palms, and the plumose bamboos; to me the most startling thina 

 was the convergence of the two types to become climbers. 



