154 EXTINCT VERTEBRATA FROM THE JUDITH RIVER 
in breadth. The posterior tooth, somewhat ellipsoidal in outline, appears, when perfect, 
to have been about 8 lines long, and is three lines wide. 
The premaxillary dental plate, (figs. 27—30, plate 11,) is irregularly lozenge-shaped in 
its vertical outline antero-posteriorly, is a little over an inch in its long diameter, 5 lines 
in its depth, and 3 lines in its greatest thickness. Its anterior border is convex, the inner 
and outer surfaces are vertical, slightly depressed planes, and the crushing surface is con- 
cave. 
Explanation of Figures, Plate 11. 
Figures 24—30. Upper maxillary plates of MyLoanaruus priscus, of the natural size. 
Figure 24. Inner view of the maxillary plate, exhibiting the surfaces of the two teeth projecting below. 
Figure 25. Oral or inferior surface of the same. 
Figure 26. Posterior extremity of the same, exhibiting the columnar structure of the teeth. 
Figures 27, 28. Outer and inner view of a pre-maxillary plate. 
Figures 29, 30. Triturating surface and upper view of the same. 
In Commodum Lectoris, Synopsis Generum et Specierum Que in hoc Opere et Alibi 
Discribuntur. 
MAMMALIA SIRENIA? 
1. IschyrorHERtum ANTIQUUM, Leidy; Proc. Acad. Nat. Sci., Phila., 1856, 89. 
SAURIA. 
2. TRACHODON MIRABILIS, Leidy: Proc. Acad. Nat. Sci., Phila., 1856, 72. 
3. Dernopon HorRiDUS, Leidy: Ibidem. 
4, PaLmoscincus costatus, Leidy: Ibidem. 
5. Troopon Formosus, Leidy: Ibidem. 
6. CrocopiLus HuMILIS, Leidy: Ibidem. 
7. THESPESIUS OCCIDENTALIS, Leidy: Ibidem, 311. 
CHELONIA. 
8. TrIONYx FOVEATUS, Leidy: Proc. Acad. Nat. Sci., Phila., 1856, 73, 312. 
9. Compsemys victus, Leidy: Ibidem. 
10. Emys osscurus, Leidy: Ibidem. 
PISCES. 
11. Lepworus occrpentauis, Leidy: Proc. Acad. Nat. Sci., Phila., 1856, 73. Lepidc- 
tus Haydeni, Leidy: Ibidem. 
12. Mytocnatuus priscus, Leidy: Ibidem, 312. 
