70 ATHERINID^: SILVERSIDES 



hybridization. Their distribution is peculiar, several closely related 

 species living together in the same lake. This rather anomalous condi- 

 tion is perhaps to be explained by the redistribution of the fish faunas 

 of the various lakes by volcanic disturbances. 



113. Chirostoma jordani Woolman, 1894.'^*- 



(Plate VI, Fig. 21.) 

 Chirostoma brasiliensis Jordan, Proc. U. S. Nat. Mus., 2, 299, 1879 (not Atherina 



BRASiLiENSis Quoy and Gaimard). 

 Chirostoma jordani Woolman, Bull. U. S. Fish Coinm., 14, 62, pi. 2, 1894; Jordan 

 and Evermann, Bull. U. S. Nat. Mus., 21, 540, 1898; Meek, Publ. Field Mus. 

 (ZooL), 3, 112, 1902; 5, 169, fig. 52, 1904; Regan, Biol. Centr.-Amcr., Pisces, 

 59, 1909 (in part). 

 EsLOPSARUM JORDANI Jordan and Evermann, Kept. U. S. Fish Comm., 330, 

 1895 (1896) ; Bull. U. S. Nat. Mus., 47, pt. 3, 2840, 1898; 4, 3157, pi. 123, fig. 

 335, 1900; Jordan and Snyder, Bull. U. S. Fish Comm., 19, 133, 1899 (1900) ; 

 Evermann and Goldsborough, ibid., 21, 152, 1901 (1902). 

 Type-locality. — Mexico City (now definitely restricted). 

 Atherinichthys brevis Steindachner, Ans. Akad. Wiss. Wien, 31, 149, 1894. 



Chirostoma breve Steindachner. Dcnk. Akad. Wiss. IVicn, 62, 526, pi. 2, fig. 2, 



1895. 

 Type-locality. — Lake Cuitzeo, Mexico. 

 Range. — Valley of Mexico, and the Lerma Basin ; in streams, canals, and lakes. 



Chirsotoma breve (Steindachner) resembles C. jordani in the 

 extreme obliquity of the gape. Contrary to Regan's view, we regard the 

 two names as based on the same species. 



A large series of jordani, including a specimen from Patzcuaro, has 

 been examined. The form of the body varies widely, in places resembling 

 C. arge. The anal rays are occasionally as numerous as I, 20. The 

 teeth are finer than in most species; those of the upper jaw appear to be 

 arranged in a narrow band ; none are especially enlarged. 



114. Chirostoma mezquital Meek, 1904.^*- 



(Plate V, Fig. 20) 

 Chirostoma mezquital Meek, Publ. Field Mus. (ZooL), 5, 170, fig. 53, 1904. 



Type-locality. — Rio Mezquital, near Durango, Mexico. 

 Chirostoma jordani Regan, Biol. Centr.-Amer., Pisces, 59, 1907 (in part). 

 Range. — Basin of the Rio Mezquital, Mexico. 



Mr. Regan's reference of this species to C. jordani is erroneous, 

 the differences indicated by Meek in his description and figure of mez- 

 quital being constant. In the nine type specimens of mezquital, the 

 mouth is decidedly less oblique than in jord.a.ni ; the body is less com- 

 pressed ; the head is less angular in either anterior or superior aspect ; 

 the origin of the spinous dorsal is farther forward (midway between 

 base of caudal and a point forward of the tip of snout, a distance vary- 

 ing from a little less than half eye, to more than length of eye). In a 

 large series of jordani from the Valley of Mexico and the Lerma 

 Basin, the origin of the first dorsal is midway between the base of the 



