eigenmann: fresh water fishes. 261 



Gunther recorded this species under the name of Tetragonoptents peten- 

 ensisixom the Rio Negro. The only recorded locality oi petenensis is Lake 

 Peten in Yucatan. Mr. C. Tate Regan has reexamined the Rio Negro 

 specimens and writes me: "I have no hesitation in referring the Rio 

 Negro specimens to Tetmgouopteriis rutilusy 



Rutilns is found from Panama (possibly Mexico) to Patagonia. 



The relation of this species to the other members of the genus is shown 

 by the following key : 



a. Anal rays 10 to 49. 



b. Lateral line 55. Anal 45 ; head 3.6; depth 2.63 ; lat. line 55. -Eye greater than snout 

 by one-third of its diameter, greater than interorbital by \-\ of its diameter. 



I. crythropterus (Holmberg). 

 bb. Lateral line with 50 scales or fewer. 

 c. Anal 40-48. 



d. Scales 42-50. 

 £. Anal 47-48. 



/. A few rudimentary teeth on the maxillary ; a silvery lateral band ; ven- 

 tral profile much arched ; snout pointed ; A. 48. Lat. line 47. 



2. spilurus Cuv. & Val. 

 ff. No teeth on the maxillary ; a very distinct silvery lateral band ; an 

 indistinct caudal and humeral spot ; maxillary reaching anterior mar- 

 gin of orbit ; depth 2.3 ; eye 3 in the head ; scales 9 or 10-47-10 

 or 1 1 ; A. 47. 3. liauxwellianus (Cope). 



ee. Anal 41-45. 



g. Scales IO-4S to 50-8 or 9 ; a small silvery lateral band ; a dark spot on 

 shoulder and another' on base of caudal ; depth 2j-2f ; A.41-45 ; 

 maxillary with a single, rather large caducous tooth ; eye 2.4 in the 

 head, about equal to interorbital. Head 4.1-4.5. 



4. pclegyini Eigenmann. 

 gg. Scales 8-42-7 or 8; A. 42 ; eye 3.7 in the head, 1.7 in the inter- 

 orbital ; head i.-j in the length ; a caudal spot. 



5. correntiniis (Holmberg). 

 dd. Scales i"] or 38. 



h. Several small teeth on the maxillary; head 3| ; depth 3 or somewhat 

 more than 3 ; snout 4 in the head ; a silvery lateral band bordered above 

 by blue-green ; a round humeral spot ; caudal spot, when present, extends 

 to the end of some of the caudal rays. A. 43 ; scales 6-37 or 38-4. 



6. bairdii (Steindachner). 



hh. Maxillary with a single, small tooth. Scales in lateral line 37 or 38 ; 



both a caudal and a humeral spot very distinct, round ; middle of caudal 



fin thickly dotted with black ; maxillary not reaching orbit ; head nearly 



4 ; depth about 2| ; A. 40-42. 7. tabaiingce (Steindachner). 



' These spots are very obscure in alcoholic specimens, while in specimens first preserved in for- 

 malin they are conspicuous and a black band replaces the silvery band of the alcoholic specimens. 



