118 
BULLETIN OF TIIE UNITED STATES FISH COMMISSION. 
ISTLARIUS Jordan & Snyder, new genus. 
Type Istlarius balsanus new species. Allied to Ictalurus and Leptops. 
Body rather deep and compressed ; head not widened nor greatly depressed ; eye large ; lower 
jaw included; teeth in villi form hands on premaxillaries and denfcaries; premaxillary hand convex 
anteriorly, with a short, angular posterior extension on each side; no division of band at symphysis; 
dentary band broad anteriorly, growing narrow and pointed posteriorly, with a distinct median 
division; no teeth on vomer or palatines; villiform teeth on upper and lower pharyngeals. Gill- 
rakers on first arch 17, long and slender ; branchiostegals 8. Air bladder very large, extending almost 
to posterior end of body cavity, divided by a transverse constriction into two parts of nearly equal 
length, the anterior part heart-shaped, posterior part oval. Supraoccipital bone widely separated 
from interspinal; humeral process short, almost hidden by the skin. Lateral line extending from 
below insertion of dorsal to caudal; skin covered with minute hair-like villi, that of head completely 
concealing bones of skull. Barbels 8. Spines with distal parts soft, not branched, continuous with 
the hard parts; basal part of pectoral spine grooved posteriorly, weakly serrate above the groove. 
Istlarius has some characters of the genus Leptops, notably the dentition of the upper jaw and the 
weakness of the fin spines, but it more closely resembles Ictalurus, and its relationship is probably with 
that genus* 
5. Istlarius balsanus Jordan & Snyder, new species. Bagre. Fig. 2. 
Type No. 6149, L. S. Jr. Univ. Mus. Locality, Rio Ixtla at Puente de Ixtla, Morelos, Mexico. Col- 
lected by Jordan & Snyder, January 3, 1899. 
Head 4 in length; depth 4.66; depth of caudal peduncle 2.33 in head; eye 5.5; snout 2.4; distance 
between eyes 2.5; height of dorsal 1.4; length of base of dorsal 3; height of anal 1.66; length of base 
of anal 1; length of pectoral 1.5; ventrals 1.66; caudal 1; D. i, 6. A. 24. 
Body deep and somewhat compressed, deepest part above ventrals, widest between pectorals; 
head narrow, not greatly depressed. Eye large, nearer to tip of snout than to posterior edge of 
opercle, a distance equal to diameter of eye; inter- 
orbital space convex ; width of mouth, 2.5 in head; 
lower jaw included ; upper jaw projecting a distance 
equal to diameter of pupil. Barbels 8; of the in- 
ferior ones, the median pair are shorter; distance 
between their bases equal to diameter of pupil; 
outer pair when extended directly backwards reach- 
ing 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 hand on upper jaw convex ante- 
riorly, with a short, angular posterior extension on 
each side; no apparent division of band at sym- 
physis; band on lower jaw broad anteriorly, narrow 
and pointed posteriorly; a distinct median division; no teeth on vomer or palatines ; upper pharyn- 
geal teeth in oval, villiform bands; lower pharyngeal teeth in 2 narrow oblong bands. Gillrakers on 
first arch 17, long and slender. Branchiostegals 8. Anterior nostril tubular, the posterior with a 
raised rim extending on each side from barbel to posterior edge of openiug, where it is divided. 
Skin of head completely concealing bones of skull. Supraoccipital bone not in contact with first 
interspinal. 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; sum 
covered with minute, hair-like villi. 
Dorsal spine with its distal third soft, preceded by a small, angular, immature spine; first and 
second branched rays longest, the others gradually shorter. Adipose fin largo, above middle of anal; 
length of posterior free edge three times diameter of pupil. Fifth or sixth anal ray longest; edge of 
fin rounded posteriorly; caudal deeply forked, lower lobe rounded, upper rather pointed. Pectoral 
rays i, 11, distal two-thirds of spine soft; not branched, continuous with the hard part; basal part 
grooved jrosteriorly, weakly serrate above the groove; ventrals reaching origin of anal. 
Color bluish-slate above, light-silvery below ; a few small dark spots on head and body ; fins with 
dusky coloring; inferior barbels light; maxillary barbels with upper half dark ; nasal barbules with 
Fig. 1. — Views showing bauds of teeth of Istlarius bal- 
sanus. (a) lower jaw, (6) upper jaw. 
