CHIROSTOMA. 57 
Synopsis of the Genera found in the Fresh Waters of Mexico and Central America. 
I. Body completely scaled ; head scaly ; maxillary not extending beyond the vertical from the 
anterior margin of eye. 
Origin of spinous dorsal in advance of the anal . . . «. . . . . . ~ J. CxrRostoma. 
Origin of spinous dorsal posterior to that of the anal . . . . . . . . «0 THyYRina. 
II. Head and anterior part of body naked . . . «. «©. . . . . . 8. XENATHERINA. 
1. CHIROSTOMA, Swains., 1839. 
Lethostole, Chirostoma, Kirtlandia, and Menidia, Jord. & Everm. Bull. U.S. Nat. Mus. xlvii. 
1896, pp. 792, 794, & 796. 
About fifteen species from the coasts of Tropical and Subtropical America, some of 
them entering rivers, and about as many fresh-water species from the Rio Lerma 
System and the Valley of Mexico. 
Synopsis of the Mexican and Central-American Fresh-water Species. 
I. Length of head 84 to 44 in the length of the fish. Jaws equal anteriorly or the lower 
projecting. Length of lower jaw less than 4 the length of head. 
A. Anal fin with I 12-15 rays; 45 to 57 scales in a longitudinal series ; 
17 or 18 gill-rakers on the lower part of the anterior arch . . . 1. bartoni. 
B. Anal fin with I 14-17 rays. 
45 to 48 scales in a longitudinal series; 20 or 21 gill-rakers on the lower 
part of the anterior arch . . . . . woe ee ww wee RD patzcuaro. 
36 to 42 scales in a longitudinal series ; 1 or 12 gill-rakers on the lower 
part of the anterior arch . . 1. 1 ee ee ee eee we Se aarge. 
C. Anal fin with I 16—21 rays. 
38 to 42 scales in a longitudinal series; 16 gill-rakers on the lower part of 
the anterior arch ; last dorsal spine above the origin of anal . . . . 4 jordan. 
38 to 45 scales in a longitudinal series; 15 or 16 gill-rakers on the lower 
part of the anterior arch; last dorsal spine in advance of the origin 
ofanal . . .. . oe woe eee ee ee ew eB Greve. 
48 to 62 scales in a longitudinal series ; ‘16 to 19 gill-rakers on the lower 
part of the anterior arch . 2. ee ee ee ee ee ee + 6. Awmboldtianum. 
68 to 82 scales in a longitudinal series . . . . 1. 1 ee ee ee eestor. 
44. to 51 scales in a longitudinal series ; 20 to 24 gill-rakers on the lower 
part of the anterior arch . 2. 2. 1 ww ee ee ee ee 8. chapale. 
56 to 62 scales in a longitudinal series; 21 to 23 gill-rakers on the lower 
part of the anterior arch... 1 1 1 ee ee ew ee we 9 grandoculis. 
II. Length of head 3$ in the length of the fish. Lower jaw shorter than 
the upper. Anal with I 19-20 rays. 53 to 56 scales in a longi- 
tudinal series . . woe eee ee ee es 10, promelas. 
BIOL. CENTR.-AMER., Pisces, May 1907. it 
