AND GREAT LIGNITE FORMATIONS OF NEBRASKA. 
151 
Though I have supposed the remains above described to indicate the former existence 
of a mammal allied to the Manatee, they yet appear to me of such a singular character, 
that I have suspected they may have belonged to an aquatic reptile, unlike any known, 
and perhaps foreshadowing in its constitution the Sea Cows, just as Iguanodon appears to 
have foreshadowed the herbivorous pachyderms of the Eocene Tertiary Period. 
Explanation of Figures , Plate 10. 
Figures 8—15. —Vertebra) and rib of Ischyrotherium antiquum; two-thirds the diameter of nature. 
Figure 8. Dorsal view of vertebral body. Articular surface on each side. 
Figure 9. Anterior view of the same vertebral body. 
Figure 10. Ventral view of a second aud similar specimen. 
Figure 11. Broken surface of a third specimen, exhibiting its dense structure and converging nutritious canals. 
Figure 12. Inferior view of a vertebral half arch and transverse process, exhibiting the articular surface, 
adapted to a corresponding one of figure 8. 
Figure 13. Anterior view of same specimen as the last. 
Figure 14. Anterior view of another specimen like that indicated in figures 12, 13. 
Figure 15. Fragment of a rib, with outline sections (16, 17,) of the size of nature, from the upper end and 
middle. 
SAURIA. 
Tiiespesius occidentalis. 
Several vertebrae, together with a first phalangial bone, from Nebraska, appear to indi¬ 
cate a deino-saurian as colossal as the Iguanodon of England, or the Iladrosaurus of New 
Jersey. Two of the specimens are exceedingly like mammalian lumbar vertebrae, espe¬ 
cially those of the Elephant or Mastodon, and might readily be taken for such, were 
it not that they possess well marked processes for the articulation of chevron bones. 
One of the vertebrae from near the trunk, and another, which I suspect to belong to the 
same animal, from near the end of the tail, together with the phalanx, were discovered 
by Dr. Hayden, in the Great Lignite Formation, at Grand River, Nebraska. Another large 
vertebra from near the trunk, was obtained by Captain Alfred Sully, U. S. A., from an 
Indian, and presented to the Academy of Natural Sciences of this city. This specimen 
Dr. Hayden supposes to have been derived from the same locality in which he discovered 
the others. 
The bodies of the two large vertebrae, viewed in front, (fig. 2, plate 10,) are quadrately 
oval in outline, and notched above; the notch corresponding with the spinal canal. One 
of them measures about 5 inches transversely and vertically; the other, 4i inches trans¬ 
versely and 4£ vertically; and their length is about 21 inches. They x are narrowed con- 
cavely from their articular borders, (fig. 1,) and are bounded below (fig. 3) by articular 
processes, for chevron bones, an inch in diameter. Their anterior articular face, (figs. 1, 
2,) is moderately convex; and their posterior face concave, with a depth of nearly 
