PLATE IV. Fig. 1. Trachodon (Pteropelyx) marginatus, Lambe, outer side of the same mandibular rainus figured on plate III; one-half the natural size. Page 73. Fig. À Trachodon (Pteropelyx) altidens, Lambe, outer side view of left maxilla, one-lialf natural size. The speciman was drawn upside down so as to have a better light on the teeth. Page 76. Fig. 3. Inner view of the same specimen, with part of the inner wall removed to show successional teeth; one-half natural size. Fig. 4. Two teeth from the same specimen, showing the characteristic border sculpture, with the crown of the worn tooth restored, in dotted outline, to show the proportion of length to breadth; twice the natural size. Fig. 5. Trachodon (Pleropelyx) marginatus, Lambe, outer view of apical part of crown of tooth from the maxilla represented on plate V, for comparison with fig. 4; twice the natural size. Page 74. Fig. 6. Trachodon (Pteropclynf) marginatus, crown of one of the teeth of the ramus shown in fig. l of this plate and fig. 1 0 f the preceding plate; twice the natural size. Page 73. Fig. 7. Pteropelyx grallllipes, Cope, crown of tooth of lower jaw, t) show border sculpture; twice the natural size. Introduced for comparison. Page 77. f, grinding surface of teeth a, facet for jugal.