O. C. Marsh—Odontornithes, or Birds with Teeth. 405 
the same, as some of the teeth preserved have the crowns of 
the successional teeth implanted in cavities in their fangs. 
modern birds. (Plate X, figures 3 and4.) The sacrum is elon- 
gated, and resembles that in recent diving birds The last 
sacral vertebra is quite small. The caudal vertebra, which are 
about twelve in number, are very peculiar, and indicate a struc- 
ture not before seen in birds. The anterior caudals are short, 
with high neural spines and moderate tranverse processes. The 
middle and posterior caudals have very long and horizontally 
expanded tranverse processes, which restrict lateral motion, but 
Clearly indicate that the tail was moved vertically, probably 
'n diving. The last three or four caudal yertebre are firmly 
coossified, forming a flat terminal mass, analogous to, but quite 
unlike, the “ ploughshare” bone of modern birds. The 
anterior two at least of these caudals have expanded transverse 
processes, 
The pelvic bones, although avian in type, are peculiar, and 
present some well marked reptilian features. resemblance 
have their posterior extremities separate. The two latter are 
) Spon free back of their union with the ilium at the 
acetabulum. The ischium is spatulate at its distal end, and the 
as rodlike. The acetabulum differs from that in all known 
irds, in being closed internally by bone, except a foramen, 
that perforates the inner wall. 
