Like all the other species of this genus it is remarkably excellent as food, the different species constituting the famous "Pescados Blancos" of the great lakes of Chapala and Patzcuaro of the western slope of Mexico. A very unusual circumstance is this: that numerous very closely related species occupy the same waters and are taken in the same nets. In zoology, generally, it is an almost universal rule that very closely related species occupy different geographical areas, their separation being due to barriers which prevent interbreeding. But in the lake of Chapala, near Guadalajara, Prof. John O. Snyder and the present writer, and subsequently Dr. S. E. Meek, found ten distinct species of _Chirostoma_, all living together, taken in the same nets and scarcely distinguishable except on careful examination. Most of these species are very abundant throughout the lake, and all reach a length of twelve to fifteen inches. These species are _Chirostoma estor_, _Ch. lucius_, _Ch. sphyræna_, _Ch. ocotlane_, _Ch. lermæ_, _Ch. chapalæ_, _Ch. grandocule_, _Ch. labarcæ_, _Ch. promelas_, and _Ch. bartoni_. A similar assemblage of species nearly all different from these was obtained by Dr. Seth E. Meek in the lake of Patzcuaro, farther south. In this lake were found _Ch. attenuatum_, _Ch. patzcuaro_, _Ch. humboldtianum_, _Ch. grandocule_, and _Ch. estor_. The lake of Zirahuen, near Chapala, contains _Ch. estor_ and _Ch. zirahuen_. [Illustration: FIG. 170.—Pescado blanco, _Chirostoma humboldtianum_ (Val.). Lake Chalco, City of Mexico. ] [Illustration: FIG. 171.—Silverside or Brit, _Kirtlandia vagrans_ (Goode & Bean). Pensacola. ]