234 DINOSAURS OP NORTH AMERICA. 



worthy differeuce from all the existing crocodiles. The hind foot, how- 

 ever, is of the crocodilian type, with the calcaueuin showing a posterior 

 projection. 



In Belodon, only the pelvis of which is here represented (fig. 62), 

 the pubis contributes a very important part to the formation of the 

 acetabulum, and to the entire pelvic arch. The latter differs from the 

 pelvis of a typical dinosaur mainly in the absence of an open acetabu- 

 lum, but a moderate enlargement of the fontanelle at the junction of 

 the three pelvic elements would practically remove this difference. A 

 more erect position of the limb, leading to a more distinct head on the 

 femur, might possibly bring about such a result. The feet and limbs 

 of Belodon are, crocodilian in type. 



Bearing these facts in mind, the diagram representing the restored 

 fore and hind limbs of the diminutive Hallonus (figs. 59-GO) shows first 



Fig. 62. — Diagram of pelvis of Belodon Kapfi von Meyer; seen from tlie left. One-fourth natural 

 size. 

 «, acetabular surface within dotted line; il, ilium; is, ischium;^, pubis. 



of all the true dinosaurian pelvis, with the pubic bone taking part 

 in the open acetabulum, and forming an important and distinctive 

 element of the pelvic arch. The delicate posterior limb and foot, 

 evidently adapted mainly for leaping, as the generic name suggests, 

 are finite unique among the Reptilia, but the tarsus, especially the 

 calcaneum, recalls strongly the same region in the orders already 

 passed in review. 



Just what this posterior extension of the calcaneum signifies in this 

 case it is difficult to decide from the evidence now known. It may be 

 merely an adaptive character, as Hallopus appears in nearly every 

 other respect to be a true carnivorous dinosaur. It may, however, be 

 an inheritance from a crocodilian ancestry, preserved by a peculiar 

 mode of life. Whatever its origin may have been, it was certainly, 



