HOLOSAURUS ABRUPTUS MARSH 353 
shows a sub-triangular facet for a firm symphysis with the opposite 
ischium. 
The pubis is much like that of Platecarpus. It is a thin bone, 
broadly rounded at the acetabular end, the posterior edge of which 
ends in facets for the acetabulum, and for articulation with the ilium 
and ischium. The pubic foramen is placed similarly to that of 
Platecarpus. The lower end of the bone is thin and somewhat 
expanded, and shows a roughened face for symphysis with the oppo- 
site pubis. 
Femur.—The femur is a heavy, stout bone, somewhat expanded 
proximally and terminating along the whole upper border in an 
articular face which is thickened anteriorly and thinned posteriorly. 
The trochanter, on the anterior side, is directed upward and inward. 
The distal end of the bone is more expanded than the proximal, and 
has a much thickened oval face for articulation with the tibia, and a 
thinner one for the fibula. 
Tibia.—The tibia is a short, stout bone, expanded and much 
thickened at the proximal end, and having a large, oval face for 
articulation with the femur. The anterior margin of the bone is 
deeply concave, and the posterior margin is longer, and less deeply 
concave. The distal end is fan-shaped, thinned anteriorly and 
posteriorly, and thickened centrally. It ends in a flat facet for articu- 
lation with the large tibial tarsal bone. 
In Plate VII of Williston’s work on the Mosasaurs,? Figs. 1 and 2 
are referred to the radius of a doubtful species of Platecarpus, but 
these bones are doubtless tibiae of Holosaurus abruptus, to which 
genus they have already been referred by Williston. 
Fibula.—The fibula is a thin, flat bone, expanded laterally at both 
ends. At the proximal end is the articulation for the femur, facing 
forward and upward. ‘The anterior margin of the bone is concave 
throughout and is shorter than the strongly concave posterior margin. 
Distally the bone is fan-shaped, and bears articular faces for the two 
upper tarsals. 
Tarsus.—The tarsus is composed of three bones, a large and two 
smaller, posterior to it, all of which are thin and flat. The large bone 
has two articular faces above, for the tibia and fibula, that for the 
t University Geological Survey of Kansas, Vol. IV, Plate LVII. 
