FAMILY XIV. ATHERINID/E. 175 



Head 4^; depth 5^3 ; D. v-io; A. 13; scales 12-54. Body elon- 

 gate, nearly terete, less compressed than in any other Chirostoma; 

 mouth moderately oblique, lower jaw slightly the longer; length of 

 snout equal to diameter of eye, 3X m length of the head; interorbital 

 broad, 3 in head; teeth very small, in a narrow band in each jaw; 

 origin of the dorsal fin nearer tip of snout than base of caudal by a 

 distance greater than diameter of eye; base of anal fin i^ in head; 

 pectoral i y$ ; ventral 2 ; scales with entire margins ; caudal peduncle 

 long and slender; gill rakers 4 + 17 = 21; vertebrae 23 + 18 = 41. 



Color dark olivaceous above, lighter below; opaque. This species, 

 characterized by its dark opaque color, its terete body, the backward 

 position of the dorsal fin, and the short anal, is one of the darkest 

 found in the Lerma basin. Length about 4 inches. It is the most 

 abundant species in Lago de Zirahuen. 



Subgenus Ohirostoma Swainson. 



162. Chirostoma humboldtianum (Cuv. &Val.). PESCADA BLANCA. 

 Atherina humboldtiana Cuvier & Valenciennes, Hist. Nat. Poiss., x, 



479> J 835; lake near City of Mexico. 

 Atherina vomerina Cuvier & Valenciennes, 1. c. ; lake near City of 



Mexico. 



Atherinichthys humboldtianus Giinther, Cat., in, 404, 1861. 

 Chirostoma humboldtianum Jordan & Evermann, Bull. 47, U, S. 

 Nat. Mus., 1896, 793: Evermann, Proc. Biol. Soc. Washington, 

 1898, 2; Laguna de Juanacatlan, Jalisco: Jordan & Snyder, 

 Bull. U. S. Fish Comm., 1900, 134; Lago de Chalco: Evermann 

 & Goldsborough, Bull. U. S. Fish Comm., 1902, 152 ; La Laguna, 

 Jalisco: Meek, Field Col. Mus. Pub. 65, 1902, 114; Chalco; 

 Xochimilco; Patzcuaro. 



Basin of the Rio Lerma and the Valley of Mexico. (Viga Canal; 

 Xochimilco.) 



Head 3^; depth 4%" to 5^; D. iv-n to 13; A. 17 to 20; scales 

 15-54. Body elongate, rather robust, not much compressed; snout 

 pointed, 3 in head; mouth moderate, lower jaw projecting; mandible 

 2 1- in head; teeth in jaws in bands, the outer slightly enlarged; occa- 

 sionally i to 3 canine teeth on vomer; eye 4 to 4^ in head; origin of 

 spinous dorsal midway between base of caudal and anterior margin of 

 eye or nostril; pectoral if; ventral 2^; scales usually cycloid, oc- 

 casionally more or less crenate; gill rakers long and slender, about 20 

 on the first gill arch; vertebrae 23 + 19=42. 



Color brownish olive, sometimes quite translucent; a narrow dark 

 silvery lateral band; specimens from lakes with much vegetation are 

 very dark. Length about 12 inches. 



