FISHES FROM THE RIVERS OF MEXICO. 
119 
light edges. Some specimens have many well-defined color-spots, while others have few or none. The 
young have no spots. Our specimens vary in length from 10 to 60 centimeters. 
Istlarius balsanus has a large and rather complex air-bladder, lying close to the spinal column and 
extending almost to the posterior end of body cavity. It is divided by a deep, transverse construction 
into two halves, The anterior part is heart-shaped and constricted dorso-ventrally. It is separated 
by a T-shaped partition into three chambers; of these, the .anterior transverse chamber is partly 
Fia. 2 . — Istlarius balsanus Jordan & Snyder, new genus and species. Type. 
divided on the median line by a fold of the dorsal wall of the bladder over the vertebral column. 
The transverse chamber is connected on each side with the two posterior lateral chambers by large 
openings in the ends of the transverse wall. The posterior half of the bladder is without partitions. 
It is connected with the left lateral chamber only, by a small opening. 
Measurements of five specimens of Istlarius balsanus. 
• 
Measurements. 
Locality: Bio Ixtla, at Puente 
de Ixtla, Morelos, Mexico. 
Length of body in millimeters 
195 
238 
148 
123 
81 
Depth of body expressed in hundredths of length 
23 
21 
19 
21 
22 
Depth of caudal peduncle 
12 
ii 
10 
Hi 
12 
26 
27 
25 
26 
27 
Length of snout 
ii 
ii 
ii 
u 
12 
Length of maxillary barbel 
21 
16£ 
19 
21 
21 
Longitudinal diameter of orbit 
4i 
5 
5 
5i 
6 
Distance from snout to dorsal 
36 
38 
37 
36 
35 
Height of longest dorsal rays 
20 
17 
17 
18 
21 
Distance from snout to adipose tin 
77 
81 
77 
79 
77 
Distance from snout to anal fin 
60 
66 
64 
02 
65 
Length of base of anal - 
26 
26 
25 
27 
26 
Height of longest anal ravs 
15i 
15 
14 
15 
16 
Length of caudal fin 
28 
25 
25 
26 
28 
Length of pectoral fin 
18 
16 
17 
17 
20 
Distance from snout to ventral fin 
51 
524 
51 
49 
52 
Length of ventral fin 
15 
14 
14 
14 
15 
Humber of dorsal rays 
7 
7 
7 
7 
7 
Number of anal rays *- 
24 
23 
21 
23 
23 
CATOSTOMID 2B. 
6. Carpiodes tumidus Baird & Girard. 
Locality, lagoons near Tampico. 
In the identification of these specimens, we regard Carpiodes tumidus Baird & Girard as a species 
distinct from Carpiodes velifer Rafinesque. The Tampico specimens agree with the description and 
figure of C. tumidus given by Baird & Girard (Baird & Girard, Proc. Ac. Nat. Sci. Phi la. 1854, 28; 
Girard, United States and Mexico Bound. Snr., Ichthyology, 34, plate xix, figs. 1-4). They all have 
the first rays of the dorsal short; in most cases the tip of the fin is rounded — in striking contrast to 
the very long rays and the scythe-shaped iiu of C. velifer of the Mississippi Valley. 
