74 ATHERINID.^: SILVERSIDES 



As Jordan and Evermann noted in 1898, the scale margins in this 

 species become laciniate with age, a character supposed to distinguish 

 the group Lethostole. The differences between humboldtianum, type 

 of Chirostoma, and estor, the type of Lethostole, are not wide, con- 

 sisting of the size of the scales, the amount of projection of the mandible, 

 and other details. We do not regard the two groups as subgenerically 

 separable. 



The teeth in C. humboldtianum are small and form a narrow 

 band posteriorly in each jaw, but anteriorly are less reduced in size, 

 and tend to assume a biserial arrangement. In one specimen at hand 

 the anterior premaxillary teeth are arranged biserially on one side, tri- 

 serially on the other. The teeth of the inner series are a little larger 

 than those of the outer series in the lower jaw, but not notably larger 

 in the upper jaw. 



121. Chirostoma regani Jordan and Hubbs, new species, 1919.-^*- 



Chirostom.\ breve Regan, Biol. Centr.-Amer., Pisces, 59, pi. 10, fig. 3, 1907 (descrip- 

 tion and figure based upon specimens originally included in the same lot as 

 that now comprising the types of C. regani; not Atherinichthys brevis 

 Steindachner). 



Chirostoma regani Jordan and Hubbs, new species. 

 Type-locality. — Xochimilco. in the Valley of Mexico. 



Range. — Lakes Xochimilco and Patzcuaro, Mexico. 



Holotype. — A mature female 94 mm. long to caudal base, collected 

 in 1901 by Dr. S. E. Meek, at Xochimilco, in the Valley of Mexico; 

 Cat. No. 3687, Field Museum of Natural History. Paratypes from the 

 same locality, some obtained in 1901, others in 1903, the longest just 

 as large as the type, are deposited in the fish collections of the Field 

 Museum and Stanford University. Other specimens from Lake Patzcuaro 

 are at hand, showing the same variations as those exhibited by the type 

 series. 



Chirostoma regani has been described and figured by Regan under 

 the name of breve, which is really a synonym of jordani. He also 

 referred the very different labarc^ to breve. C. regani is perhaps 

 most closely related to humboldtianum, but differs from that species 

 in its smaller size, larger and more completely crenate scales, shorter 

 and blunter snout, smaller eye, etc. From patzcuaro, a species of 

 similar size, it is distinguished by the same proportional dift'erences. 

 and by the more posteriorly inserted first dorsal. It has finer scales, a 

 smaller eye, etc., than grandocule. It differs from chapal^, to which 

 it is also closely related, in the firmer flesh, less compressed body, 

 convex lower margin of mandible, less oblique maxillary, fewer gill- 

 rakers, and fewer anal rays. 



