AND GREAT LIGNITE FORMATIONS OF NEBRASKA. ibys 
their exterior surface being closely studded with uniform granular tubercles, which give 
to them a shagreened appearance, quite different from any thing I have had the opportu- 
nity of seeing in other turtles. 
Explanation of Figures, Plate 11. 
Figures 5, 6, 7. Fragments of plates of the carapace of CompsEMys VIcTUS, of the natural size. The cara- 
pace represented as partially but ideally restored, with the relative position of the fossil fragments. 
Figure 5. A vertebral plate. Figure 6. A portion of a right costal plate. 
Figure 7. Marginal view of the same specimen as the last, giving an idea of the curvature of the carapace. 
Emys OBSCURUS. 
Associated with the remains of Compsemys, and fragments of the shell of another tur- 
tle previously mentioned as not being distinguishable from those of Trionyx foveatus, Dr. 
Hayden found fragments of a carapace, sufficiently characteristic only to determine that 
they indicate a species of Hmys.- The best of the fragments, represented in figure 4, plate 
11, consists of the greater portion of a costal plate, which is sixteen lines wide, a line and 
a half thick, and in its perfect state may have been about five inches long. 
Explanation of Figure, Plate 11. 
Figure 4. Fragment of a right costal plate of EMys opscurus; restored in outline. 
FISHES. 
MYLOGNATHUS PRISCUS. 
The very singular-looking fish, Chimera, of the European seas, was represented during 
the Miocene period in Nebraska, by a genus for which the above name has been proposed. 
Its former existence is indicated by specimens of dental plates, like those of Chimera, 
adapted to the crushing of mollusca and crustacea, used as food. The specimens, consist- 
ing of an upper maxillary and a premaxillary plate, were obtained by Dr. Hayden from 
the Great Lignite Basin near Long Lake, Nebraska. 
The upper maxillary plate, (figs. 24, 25, 26, plate 11,) consists of a narrow triangular 
bone, containing two teeth. The specimen is broken at its two extremities, and when 
perfect appears to have been a little over an inch in length. Its posterior part is 3% lines 
wide, and about 42 lines thick. The free convex surfaces of the peculiar porous teeth, 
occupy nearly the entire length and breadth of the bone, (fig. 25, plate 11,) and are sepa- 
rated from each other by an oblique, linear tract. The anterior tooth is lozenge-shaped 
in outline, and when perfect appears to have been about 2 an inch in length, and 14 lines 
