HYODONTIDZ. 67 
white. This produces a peculiar feature of coloration singular in this 
family, resembling in some slight degree that of the Cyprinodont genus 
Aiphophorus. 
Types: Two specimens, numbered 16928 in the United States National 
Museum; collected by Mr. Fred. Mather in the Tangipahoa River, in 
Louisiana. The larger specimen is 10 inches long. 
HYODONTID ZA. 
52. HYODON SELENOPS, Jordan & Bean, sp. nov. 
Three well-marked species of the genus Hyodon inhabit the fresh 
waters of the United States, viz: Hyodon chrysopsis Richardson, of the 
water-basins of the Saskatchewan and Upper Missouri; Hyodon tergisus 
Le Sueur, the common ‘“ Moon-Eye” of the Great Lake region and Upper 
Mississippi; and an undescribed species for which the name of Hyodon 
selenops is suggested, inhabiting the waters of the Southern States. The 
various synonyms, Hyodon clodalus Le Sueur, Abramis smithii Rich., 
Hyodon amphiodon, alosoides, heterurus, and vernalis Raf., evidently be- 
long to the common Hyodon tergisus, so that the proper nomenclature of 
these species is a simple matter. 
Hyodon selenops is distinguished from the others by the more elongate 
body, which is less compressed than usual, and there is less difference 
between the curve of the back and that of the belly. The belly anterior 
to the ventral fins is transversely rounded, or even almost flattened 
instead of being obtusely carinated as in H. tergisus, or sharply carinated 
as in H. chrysopsis. 
So strongly do H. selenops and H. chrysopsis differ in this respect that 
they would be considered as belonging to different genera were not,the 
intermediate type H. tergisus still extant. Prof. Gill considers that, in 
the interests of conciseness of expression, the modifications of structure 
in the group should be expressed by at least subgeneric appellations, 
and in this I concur with him. Prof. Gill and myself, therefore, pro- 
pose the new subgeneric term Elattonistius (2jdctrov, smaller; ¢sttos, 
banner—i. e., dorsal fin) for the Hyodon chrysopsis, and assign the char- 
acters given in the annexed synopsis. The scales are much less closely 
’ imbricated in H. selenops, and the number of series is, therefore, fewer. 
The dorsai fin is comparatively large, and nearly as long as high in front 
as in H. tergisus, and the pectoral fins are short, as in the latter species. 
But the most striking difference is in the size of the eye, which is exceed- 
