. Bulletin. Natural history. RUSSELL: AMERICAN MOSASAURS 99 The ilium is constricted into a long, slightly anterior-inclined shaft im- mediately above the acetabular facet. The shaft is straight in Tylosaurus, but the distal end curves more directly upward in CUdastes, M. conodon, Amphckepitbis (Mehl, 1930), and is short and nearly straight in Platecarpus. The shaft is elliptical in anteroposterior cross section and was probably suspended between the vertical sheet of the M. supracostalis anteriorly and that of the M. iliocaudalis posteriorly. The ilioischiadic ligament probably inserted somew
. Bulletin. Natural history. RUSSELL: AMERICAN MOSASAURS 99 The ilium is constricted into a long, slightly anterior-inclined shaft im- mediately above the acetabular facet. The shaft is straight in Tylosaurus, but the distal end curves more directly upward in CUdastes, M. conodon, Amphckepitbis (Mehl, 1930), and is short and nearly straight in Platecarpus. The shaft is elliptical in anteroposterior cross section and was probably suspended between the vertical sheet of the M. supracostalis anteriorly and that of the M. iliocaudalis posteriorly. The ilioischiadic ligament probably inserted somewhere near the center of the posterior border, as it cloes in Varanus. Origins of the Mm. iliofibularis, iliofemoralis and iliotibialis were probably compressed into the posterior, central and anterior portions, respectively, of the ventrolateral region of the shaft. The iliopubic ligament must have inserted somewhere near the ventral end of the anterior edge. The distal end of the iliac shaft is abruptly truncated in CUdastes, M. conodon, Platecarpus and Tylosaurus and was prob- ably attached by ligaments to the transverse process of the first pygal (sacral) vertebra. In Amphekcpubis the ilium seems to have tapered to a point distally. PUBIS The pubis is approximately the mirror image of the ischium in shape, al- though it is longer and more strongly directed anteromedially. In CUdastes and Mosasaurus conodon the head of the pubis is divided into three subequal facets, a dorsoposterior one for the ilium, a posterior one for the ischium and a con- cave acetabular facet laterally. As in the other pelvic elements these facets are only indistinctly separated in Amphekepubis (Mehl, 1930, pi. 65 fig. 1), Plate- carpus and Tylosaurus. Just medial to the head, the body of the pubis constricts in an anterolateral-posteromedial direction and then curves more directly medially into a long spatulate shaft. In many mosasaurs a stout process arises from the anterior border of the pubis near
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