Jordan and Evcrmann. Fishes of North America. 3139 



distal parts soft, not branched, continuous with the hard parts; basal 

 part of pectoral spine grooved posteriorly, weakly serrate above the 

 groove. 



Istlar'ms has some of the characters of the genus Leptops, notably the 

 dentition of the upper jaw and the weakness of the fin-spines; but it 

 morn closely resembles Ictalurus, and its relationship is probably with 

 that genus. 



(Named for the Rio Ixtla, the type locality of the type species.) 



20S (a). ISTLARIUN BALSAM'S, Jordan &. Snyder. 



Head 4; depth 4; depth of caudal peduncle 24 in head; eye 54; snout 

 2;; distance between eyes 24; height of dorsal Ijj-j length of base of 

 dorsal 3; height of anal If; length of base of anal 1; length of pectoral 

 14; veutrals If; caudal 1; D. I, 6; A. 24. Body deep and somewhat com- 

 pressed, deepest above ventrals, widest between pectorals; head narrow, 

 not greatly depressed; eye large, nearer tip of snout than to posterior 

 edge of opercle a distance equal to diameter of eye; iuterorbital space 

 convex; width of mouth 24, in head, lower jaw included; upper jaw pro- 

 jecting a distance equal to diameter of pupil; barbels 8; of the inferior 

 ones the median pair shorter; distance between their bases equal to the 

 diameter of pupil; the outer pair when extended directly backward reach 

 the edges of gill covers ; maxillary barbels longest, reaching upper angle 

 of gill opening; nostril barbels reaching middle of pupil. Teeth in broad 

 villiform bands on premaxillaries and dentaries, the band on upper jaw 

 convex anteriorly, with a short, angular posterior extension on each side, 

 no apparent division of the baud at symphysis; band on lower jaw broad 

 anteriorly, narrow and pointed posteriorly, a distinct median division; 

 no teeth on voiner or palatines ; upper pharyngeal teeth in oval villiform 

 bands; lower pharyngeal teeth in 2 narrow oblong bands; gill-rakers 

 on first arch 17, long and slender; brauchiostegals 8; anterior nostril 

 tubular, the posterior with a raised rini extending 011 each side from the 

 barbel to the posterior edge of the opening, where it is divided; skin of 

 head completely concealing the bones of skull; supraoccipital bone not 

 in contact with interspiual; humeral process about as long as vertical 

 diameter of eye, almost hidden by the thick skin; lateral line extending 

 from a perpendicular through insertion of dorsal to caudal; skin covered 

 with minute, hair-like villi; dorsal spine with its distal third soft, pre- 

 ceded by a small, angular, immature spine; first branched ray longest, the 

 others gradually shorter; adipose fin large, above middle of anal; length 

 of the posterior free edge 3 times diameter of pupil; third or fourth anal 

 ray longest, edge of fin rounded posteriorly ; caudal deeply forked, the 

 lower lobe rounded, the upper rather pointed; pectoral rays I, 11, distal 

 two-thirds of spine soft, not branched, continuous with the hard part: 

 basal part grooved posteriorly, weakly serrate above the groove ; veutrals 

 reaching origin of anal. Color bluish slate above, light silvery below; a 

 few small dark spots on the head and body; fins with dusky coloring; 

 inferior barbels light; maxillary barbels with upper half dark; nasal 

 barbules with light edges. Some specimens have many well-defined color 





