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EXTINCT VERTEBRATA FROM THE JUDITH RIVER 
2. Extinct Vertebrata from the Great Lignite Formation. 
MAMMALIA SIRENIA? 
ISCHYROTHERIUM ANTIQUUM. 
Among the most enigmatic fossil remains of vertebrata collected by Dr. Iiayclen, in Ne¬ 
braska Territory, are a number of fragments of bones, obtained from an out-lyer of the 
Great Lignite Tertiary Formation, between the Moreau and Grand Rivers. 
The specimens consist of two vertebral bodies, the half of a third one, two apparent 
transverse processes, and numerous fragments of ribs. We cannot positively determine 
the affinities of the animal represented by these bones, but from their solidity of structure 
and the cylindroid form of the ribs, we suspect Ischyrotherium to be more nearly allied to 
the Manatee than to any other known animal. 
The vertebral bodies, (figs. 8—11, plate 10,) apparently posterior dorsal, are segments of 
a cylinder compressed from above downward, so that their articular faces are transversely 
oval in outline. They are comparatively slightly constricted at the middle; and in this 
position present a number of orifices of large vascular canals, which converge to the cen¬ 
tre of the bodies. Both articular faces are slightly concave, with obtuse margins. The 
dorsal surface, (figure 8, plate 10,) exhibits a narrow tract corresponding with the spinal 
canal, and on each side, a broad, concave, porous articular surface for conjunction with 
the sides of the vertebral arch. 
The broken vertebral body, (figure 11, plate 10,) presents an equally dense structure 
throughout, except at the articular surfaces, which are finely porous. The large vascular 
canals are seen in this specimen converging from the middle circumference to the centre of 
the bone, and smaller ones are observed pursuing a like course from the borders of the ar¬ 
ticular surfaces. 
The specimens of transverse processes, (figs. 12, 13, 14, plate 10,) are remarkable for 
their robust character and cylindroid form. The outer extremity of the longer specimen, 
though abruptly truncated, appears nevertheless to be entire. The inner extremity of the 
specimens, inferiorly, presents a broad, convex, porous, articular surface, for conjunction 
with the corresponding surfaces of the vertebral bodies. Above this surface, there is a 
smooth arching one forming the side of the vertebral canal and overhung by the abut¬ 
ment for the articular and spinous processes. 
The numerous fragments of ribs, generally indicate these bones to have a curved fusi¬ 
form shape, as seen in fig. 15, plate 10, representing one of the more perfect specimens. 
In structure they exhibit the same remarkable solidity noticed in the corresponding bones 
of the Manatee. 
