FISHES FROM THE RIVERS OF MEXICO. 
145 
fourth rays longest, united at their tips, forming a slender filament. The tip of anal extends a little 
farther posteriorly than that of dorsal. Caudal rounded. Tip of pectoral rounded. Ventrals located 
slightly posterior to bases of pectorals, extending to vent; outer ray longest, ending in a filament. 
Color dark; an oblong brownish-black spot at base of each scale on sides of body, the spots 
growing less distinct above the pectorals; membranes of dorsal, anal, and caudal with small spots, 
these more distinct and regularly arranged on soft parts of dorsal and anal: pectorals and ventrals 
Pis. 21 . — Her os istlanus Jordan & Snyder, new species. Type. 
without spots. Young individuals have a browuish-black spot at base of caudal aud on side of body at 
tip of pectoral, a less distinct spot at upper edge of gill-opening and also below posterior end of base 
of dorsal. The darker of these spots is sometimes faintly indicated on the larger individuals. 
The annexed table shows the variations of some of the characters of the type and cotypes. 
Measurements of ten specimens of Heros istlanus. 
Measurements. 
Locality : Rio Ixtla at Puente de Ixtla, 
Mexico. 
Morelos. 
Length of body in millimeters 
131 
129 
122 
117 
112 
107 
77 
55 
43 
29 
Depth of body expressed in hundredths of 
length 
39 
37 
38 
38 
35 
41 
40 
35 
38 
40 
Depth of caudal peduncle 
15 
14 
144 
15 
14 
15 
16 
15 
14 
15 
Length of head 
35 
35 
35 
35 
36 
37 
37 
37 
36 
39 
Width of interorbital space 
11 
10 
10 
10 
10 
11 
10 
9 
9 
10 
Length of snout 
15 
15 
14 
15 
16 
15 
15 
14 
14 
13 
Diameter of orbit 
n 
71 
8 
7 
IX 
8 
9 
9 
10 
12 
Distance from snout to dorsal fin 
43 
41 
40 
42 
42 
43 
42 
42 
43 
44 
Height of longest dorsal spine 
13 
134 
15 
14 
15 
16 
16 
13 
16 
15 
Height of longest dorsal ray 
25 
30 
24 
25 
26 
27 
26 
24 
24 
18 
I )istance from snout to anal fin 
68 
68 
67 
70 
71 
70 
70 
68 
69 
65 
Heightof longest anal spine 
14 
13 
16 
14 
13 
15 
16 
16 
14 
15 
Height of longest anal ray 
30 
26 
28 
26 
25 
28 
25 
23 
23 
20 
Distance from anal to caudal fin 
1C 
16J 
16 
16 
15 
16 
16 
18 
15 
16 
Length of caudal fin 
31 
28 k 
31 
30 
28 
31 
31 
29 
28 
25 
Length of pectoral fin . 
23 
25 
26 
25 
23 
25 
26 
25 
26 
25 
Distance from snout to ventral fin 
42 
40 
40 
42 
44 
42 
44 
43 
43 
44 
Length of ventral fin 
27 
24 
27 
24 
23 
25 
24 
24 
23 
21 
Number of dorsal spines 
10 
16 
16 
16 
16 
16 
16 
15 
16 
16 
Number of dorsal rays 
10 
11 
11 
10 
10 
10 
10 
10 
10 
10 
Number of anal spines 
5 
5 
6 
5 
5 
5 
5 
5 
6 
5 
Number of anal rays 
7 
8 
8 
7 
8 
7 
7 
7 
7 
7 
Number of scales in lateral line 
28 
28 
28 
27 
27 
28 
27 
30 
28 
27 
Number of scales in transverse series 
18 
18 
17 
17 
17 
17 
16 
17 
16 
16 
P. C. B. 1899—10 
