148 FIELD CoLUMBIAN MusEUM—GEOLOGY, VOL. II. 
ilium extends a short distance beyond the end of the sacrum as a short, 
obtuse process. It sends an angular expansion upward and inward 
opposite the end of the sixth sacral vertebra, which extends five or six 
millimeters above the margin of the sacrum, possibly forming a sort. of 
roof over the last sacral and the first caudal, and approaching, or 
possibly meeting, its mate in-the middle. The flattened or ventral por- 
tion (Pl. XLI, Fig. 1, 7) of the ischio-pubis is somewhat trapezoidal in 
shape with the symphysial line slightly oblique to the sacral border. 
Both bones, separated at the median suture, lie with the visceral surface 
uppermost, and both present a considerable concavity. The anterior 
border begins at the upper margin of the process, which articulates with 
the sutural surface described on the lateral margins of the sacrum oppo- 
site the first intercostal foramen. ‘The margin is thin and concave as far 
as the angular process for the attachment of the prepubis. This process 
is everted from the brim of the pelvis, and is tipped with a small, oval, 
cartilaginous or articular surface. From this surface the margin, some- 
what thicker, recedes in a straight line to the beginning of the median 
symphysis. The symphysial margin is thin and nearly straight. For 
the first fourth of its length it seems to meet its mate, if at all, in an 
harmonious suture, and the symphysis in front may have been somewhat 
rounded or subangular; beyond this, however, the two bones meet in a 
very oblique surface, attaining a width of four or five millimeters poste- 
riorly, and the two bones must have formed a thin and sharp keel when 
conjoined. The posterior border is somewhat thicker than the anterior 
one. It begins in a rather acute rounded angle at the base of the 
posterior process of the ilium, and is directed backward and ventrad to 
the angular extremity of the symphysis. The large rounded ischiadic 
(obturator) foramen is situated in front of the middle of the bone, 
almost directly ventrad to the acetabulum; its borders are smooth and 
thin. Between this foramen and the margin of the ilium, there is a con- 
siderable convexity, representing the floor of the acetabulum. Its dorsal 
margin must be nearly over the line of the sacrum. The junction of the 
innominate with the sacrum is by a narrow concave sutural surface, fitting 
on the margin of the sacrum; in front there is a considerable oval surface 
on the anterior part of the bone, which fits into the depressed surface 
already described, on the sides of the sacrum. Posteriorly, also, the pro- 
jection of the ilium has a little broader attachment. Dorsad to this 
junction the ilium seems to have projected beyond the margin of the 
sacrum slightly in the middle, expanding in the angular process already 
described. 
Prepubes. Pl. XLI, Fig. 1, ff. The prepubes are very nearly as they 
are in Preranodon, consisting of a flat, transverse ribbon-like band meet- 
