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On the Extremities of Tylosaurus. 
BY S.) W. WILLISTON. 
With Plates IX-XII. 
All that has been published hitherto concerning the extremities 
of this genus of saurians are the figures of the femur by Marsh*, of 
the humerus, femur, tibia, fibula and various: phalanges by Cope 
(Cret. Vert.) and a sketch of the front paddle by Professor F. H. 
Snow. t 
The specimen figured by Chancellor Snow—one of the best of 
the order in our collection—has since been more thoroughly cleaned 
from the matrix, enabling a more accurate drawing to be made, 
which is presented herewith. This paddle is the most perfect that 
I have ever seen in any specimen from the Kansas Cretaceous, and 
determines some interesting points about which there has been 
doubt hitherto. A photographic reproduction of the paddle is 
given in plate IX, as it lies upon the chalk slab. The parts there 
concealed beneath the ribs and vertebre have been carefully laid 
bare from the opposite side and their position is shown in the ac- 
companying outline figure. 
This specimen, it will be remembered, is the one in which the 
excellent casts of the skin are preserved, a figure of which was 
given by Snow in the paper cited. This engraving is so accurate, 
that, together with a photographic reproduction of a portion of the 
cast, (plate XII) additional description is unnecessary. A compari- 
son of the scales with those of the Monitor, from the same region 
of the body, shows them to be remarkably alike, both in size and 
shape. 
The position of the paddle is evidently a natural one and the fact 
is of interest as showing the general expansion and general curva- 
ture of the digits. The lmb is undoubtedly more flexible than is 
the case with either C//dastes or Mosasaurus, as is shown by the 
considerable space between the different bones, which while partly 
filled out with cartilage, must have left very free articulations. 
*Amer. Journ. Sci., 1872. 
+Trans. Kans, Acad. Sci., Vol. vi, p. 54, 
(99) KAN, UNIV, QUAR., VOL, VI, NO. 2, APRIL, 1897, SERIES A, 
