290 PROCEEDINGS OF THE XATIOXAL MUSEUM. vol.52, 



knowledge of the species in displaying charticters already observed, 

 but it is interesting for the same reason that the young of other species 

 are interesting to which we have called attention in the present article 

 and figured in plate 14 — namely, immature examples of Belonosto- 

 mus, Notagogus, and Acanthurus (pi. 14, fig. 1) (the last from the 

 upper Eocene of Monte Bolca, Italy). These young individuals 

 acquaint us with early growth stages of the several species in question, 

 and enable us to compare the relative proportions of different parts 

 at different periods in the life history for the species in question. The 

 original of our plate 15, figure 2, is catalogued as No. 6037. 

 Formation arid locality. — Green River Eocene, Wyoming. 



Family CYPRINODONTIDAE. 



In this family, which includes forms of extremely small size, the 

 mouth is protractile, teeth are present on the jaws and pharyngeals, 

 but rarely on the palate; the palatoquadrate arch is more or less 

 reduced; and the supraoccipital extends forward to the frontals, 

 separating the parietals in the median line. Only two or three 

 extmct genera are known with certainty. Modern forms are mostly 

 confined to fresh waters, but a few are found in brackish water and on 

 the soacoast. 



Genus GEPHYRURA Cope. 



In July, 1891, E. D. Cope published descriptions of five new species 

 of fossil fishes from a supposed Lower Tertiary horizon in Roe Hills, 

 South Dakota. Tliree of the forms were regarded as typical of new 

 genera, which were named by the author GepJiyrura, Prohallostomus, 

 and OligoplarcTius; the taxonomic relations of the fu'st two being with 

 the cyprinodonts, and of the last named with the percoids. The 

 holotypes of these now genera and species are now preserved in the 

 American Museum of Natural History and have recently been studied 

 by the present WTiter. Although the type of GepJiyrura was referred by 

 Cope with some hesitation to the cyprinodonts, there does not appear 

 to be the slightest doubt as to the correctness of this association; and 

 the unique specimen available for study evidently stands in close 

 relations with the new cyprinodont genus immediately to be de- 

 scribed from the Lahontan beds near Hazen, Nevada. For conven- 

 ience of rcferrence, however, we may fij'st restate the specific char- 

 acters of G. concentrica, as defined by Cope. 



GEPYRURA CONCENTRICA Cope. 



Gephyrura concentrica Cope, Amer. Naturalist, vol. 25, 1891, p. 654. 



Char, specif. — The only specimen is broken vertically across the middle, and the 

 posterior half shifted so as to lie immediately below its proper position. It appears 

 that little or no pait of the fish has been lost. Eadii, P. 9; D. 9; C. 6-16-8; A. II 11. 



