io8 Field Columbian Museum — Zoology, Vol. III. 



This species differs from X. hellcri in the more forward 

 position of the ventrals, the longer caudal appendage of males, 

 the larger eye, the more uniform coloration of females and the 

 spotted dorsal of the females. 



Viviparous; one female 2.40 inches with 39 young, the young 

 coiled about the egg-sack; a slightly larger female contained 47 

 young. 



Our specimens were collected on May 9, 1901. The young 

 are probably deposited from the middle to the last of May. 

 Jalapa. 



ATHERINID^. 



Recent studies of the fresh water fishes of Mexico have resulted in 

 the discovery of a large number of species of this family, nearly all of 

 which are found in the Valley of Mexico and in the Lerma Basin. At 

 present no species of this family is known from streams on the Atlan- 

 tic side between the Rio Grande and Catacoalcos. Those found in 

 the Lerma Basin and in the Valley of Mexico belong to one genus. 

 So far we do not know any species of this genus from other streams 

 and lakes in Mexico. 



KEY TO THE GENERA OF ATHERINIDyE. 

 a. Origin of spinous dorsal in advance of the origin of the anal 

 fin; iris silvery, base of anal tin equal to or shorter than the length 

 of the head. ■ chirostoma. 



. aa. Origin of spinous dorsal behind origin of anal fin; iris black; 

 scales with slightly crenate edges. 38 in the lateral line; base of anal 

 fin \ longer than head, its rays 22 in number. (Species of small size.) 



MELANIRIS. 



CHIROSTOMA 'Swainson. 



The species of this genus fall into three groups, though not suffi- 

 ciently marked to separate them into three distinct genera. It seems 

 to me more logical to regard C. jordani as the only species referable 

 to Eslopsannn. It has a more compressed body, larger scales, a 

 very short snout and very oblique mouth. Vertebras 21 -f- 17 — 38. If 

 this be done then Chirostoma would be restricted to all other species 

 with scales having entire margins. This would include arge, bartotii, 

 atienuatum, laharcce, patzcuaro, zirahuen and humboldtianujii, six species 

 of small size and one of large size; scales from 40 to 54; vertebrae 36 

 to 44; gill-rakers 14 to 25. 



The third ^xow^^^Letliostole would include the eight remaining 



