HYODONTID^. 67 



white. This produces a peculiar feature of coloration singular in this 

 family, resembling in some slight degree that of theCyprinodont genus 

 Xiphophorus. 



Types : Two specimens, numbered 16928 in the United States National 

 Museum ; collected by Mr. Fred. Mather in the Tangipahoa Eiver, in 

 Louisiana. The larger specimen is 10 inches long. 



HYODONTID^. 



53. 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 Eichardson, of the 

 water-basins of the Saskatchewan and Upper Missouri ; Hyodon tergisu& 

 Lb 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 dodalus Le Sueur, Ahramis 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 cariuated 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 {eXdrrw, smaller; i<;rwq, 

 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 iZ. selenops, and the number of series is, therefore, fewer. 

 The dorsal 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- 



