FAMILY III. 



Color yellowish, greenish, or blackish, very variable. Length 12 

 to 1 8 inches. 



The most southern record for this species is the Rio Grande at 

 Brownsville, Texas. It is the only member of the family found in 

 Mexico which does not have a decidedly forked tail. 



6. Istlarius Jordan & Snyder. 



Istlarius Jordan & Snyder, Bull. U. S. Fish Comm., 1900, 118. 

 (Type, Istlarius balsanus Jordan & Snyder.) 



Body elongate, somewhat compressed; teeth in villiform bands 

 in both jaws, the one in the upper jaw with an angular posterior ex- 

 tension on each side; band of teeth in lower jaw with a median divi- 

 sion growing narrow and pointed posteriorly ; gill rakers long and slen- 

 der, 1 7 on first gill arch ; barbels 8 ; skin completely covering the head ; 

 supraoccipital bone widely separated from interspinal; humeral 

 process short, almost hidden ~by the skin; adipose fin with its pos- 

 terior margin free. 



14. Istlarius balsanus Jordan & Snyder. BAGRE DEL BALSAS. 



Istlarius balsanus Jordan & Snyder, Bull. U. S. Fish Comm., 

 1900, 118; Rio Ixtla, Puente de Ixtla, Morelos: Jordan & Ever- 

 mann, Bull. 47, U. S. Nat. Mus., 1900, 3138: Meek, Field Col. 

 Mus. Pub. 65, 1902, 72; Puente de Ixtla; Balsas. 

 1 Basin of the Rio Balsas. (Cuautla; Jojutla.) 



FIG. 2. JAWS SHOWING TEETH OF ISTLARIUS BALSANUS Jordan & Snyder. 



Head 4; depth 4^3; D. i, 6; A. 24. Body oblong, deep, some- 

 what compressed; head narrow, not greatly depressed; upper jaw 

 the longer; eye small, 5> in head; distance from tip of snout to origin 

 of dorsal fin 2 y^ in body; tips of maxillary barbels reaching slightly 

 past base of pectoral ; pectoral spine slightly serrate on inner margin ; 

 anal fin long, its base equaling length of head; caudal fin forked, the 

 lobes equal; caudal peduncle robust, its least depth 2^3 in the head. 



