12 MOSASAURUS. 
“a 
slightly depressed planes, and the inner one is strongly striate at base. The bottom 
of the exposed pulp cavity of the crown is two lines and a half by one line and 
three-quarters in diameter. . 
34. Two imperfect specimens of teeth, obtained by Dr. Hayden from the Creta- 
ceous formation Number 4, at the mouth of White River, Nebraska. One of them, 
represented in Fig. 18, Plate X, is the shed crown of a small tooth, resembling the 
preceding, except that it is sightly narrower in proportion to its length, and the 
surfaces, though generally more striate, are almost devoid of subdivisional planes, 
especially the inner one. Its length is ten lines, the antero-posterior diameter of 
the oval base four lines and three-quarters, and the transverse diameter four lines. 
The second specimen, Fig. 19, consists of portions of both fang and crown of a tooth, 
which appears to have resembled the former one. 
35. ‘The fragment of an upper jaw of the right side received for examination from 
the Museum of the Smithsonian Institution. It is labelled Leiodon, from near 
Marion, Alabama, and the adherent matrix indicates that it had been imbedded in 
a soft cream-colored limestone, resembling the coarser varieties of chalk. It measures 
four inches along the alveolar border, and contains three fangs, from which the 
crowns have been broken off. The outer surface is longitudinally straight, vertically 
convex, and is rough. About an inch above the alveolar border it exhibits a trans- 
verse row of vasculo-neural foramina communicating with a dental canal within. 
The intermediate of the three fangs preserved in the specimen is deeply excavated 
in the usual manner and contains the crown of a successional tooth. The latter, 
represented in Fig. 7, Plate XIX, is about ten lines long, and agrees in form with 
those ascribed to Leiodon. 
36. A supposed pterygoid bone, previously indicated, from near Columbus, Mis- 
sissippi, discovered by Dr. Wm. Spillman, together with vertebra, a humerus, and 
other remains of a Mosasauroid Reptile, already described. The specimen is repre- 
sented in Fig. 14, Plate XI; and I suppose it to be the greater portion of the left 
pterygoid. It bears some resemblance to a fragment of the lower jaw of a Lepidos- 
toid Fish, and clearly indicates a species, if not a genus, distinct from the more 
familiar Mosasaurus of New Jersey. 
The fragment is broken at both ends, though the anterior one appears to be 
~ nearly complete ; and in its present state it measures three inches long. The outer 
border is broken, and the upper transversely convex surface, over an inch in breadth, 
is also mutilated» The inner border forms a narrow ledge defining the lower from 
the upper surface. 
The specimen contains five teeth, a vacant alveolus, and portions of two others 
at the extremities, so that the complement of teeth appears to have accorded with 
that of the pterygoid series of the great Mosasaurus. The crowns are sustained on 
large osseous pedestals, as in the latter, but instead of being lodged in deep sockets 
they are rather arranged in a series occupying a broad groove; the fangs being 
coossified with each other, with the outer parapet of the bone, and the bottom of the 
groove, leaving the inner sides for three-fourths their length exposed. 
The anterior four teeth successively increase in size, are then followed by a 
capacious vacant socket, and then by another tooth as large as the fourth one. 
