AND GREAT LIGNITE FORMATIONS OF NEBRASKA. 147 
In structure, the tooth appears wholly composed of dentinal substance, and exhibits 
no trace of enamel upon the crown. 
A proportionate increase in length of Pul@oscincus with the size of the teeth, in com- 
parison with those of Iguana tuberculata, would give the animal a length of over thirty 
feet, which is however not probable, as we observe no necessary relation of length of ani- 
mals in proportion with the size of their teeth. 
In the same formation from which the tooth of Puleoscincus was obtained, there were 
found about a dozen vertebral bodies, which may belong to the same animal, and if this 
is the case, we may obtain from them a more just idea of the size of the latter. These 
vertebral bodies are cylindroid, comparatively slightly constricted, and have the extremi- 
ties slightly concave. In the true Iguanas the vertebral bodies have a totally different 
form, as they interlock with one another by a ball and socket joint; this, however, is no 
positive evidence that the fossil specimens do not belong to Pal@oseincus. Some of these 
vertebrae are represented in figures 56 —61, and they measure from 7 to 9 lines in length. 
Accompanying the vertebral bodies, there is an ulna, represented in figure 8, plate 11, 
which is solid, and perhaps belongs to the same animal. 
Paleoscincus, probably like the marine Amblyrhynchus of the Galapagos Islands, was 
aquatic and fed upon plants. 
Explanation of Figures, Plates 9, 11. 
Figures 49—52. Tooth of PALmosciNcUS CosTATUS; magnified two diameters. 
Figures 49, 50. Outer and inner views. 
Figure 51. Apparently the forward view. 
Figure 52. Section at the broken extremity of the specimen. 
Figures 56—61. Vertebree; of the size of Nature. 
Figure 56. Anterior view of a dorsal vertebral body. 
Figure 57. Lateral view. 
Figure 58. Anterior view of an anterior caudal vertebra. 
Figure 59. Lateral view. 
Figure 60. Anterior view of a posterior caudal vertebra. 
Figure 61. Lateral view. 
Figure 8, plate 11. An ulna, natural size, suspected to belong to Paleoscincus costatus. 
TROODON FORMOSUS. 
In association with the remains previously described from the Judith River, Dr. Hay- 
den discovered the tooth of a large Monitor, to which the above name has been applied. 
Probably aquatic like many of the living Monitors, the voracious 7’roodon was most likely 
a troublesome enemy to the peaceful plant-eating Pal@oscincus. 
