1914] The Ottawa Naturalist. IS 



gives digit I a forwardly rather than a backwardly directed 

 position in the foot, The vestigial proximal end of metatarsal 

 V is in place in each leg, recalling to mind a similarly reduced 

 I'one in Ornithomimiis alius, Lambe, also from the Belly River 

 formation of Alberta. 



Each abdominal rib consists of two well ossified, flattened 

 lengths, which overlap at their inner ends. Outwardty, each 

 lateral half is slightly grooved on its front margin for the recep- 

 tion of a slender rod-like bone (supplementary), which lies 

 closelv against the rib and projects but slightly beyond its outer 

 end. 



The four premaxillary teeth are remarkably long and slender, 

 with a keel on each side of a slightly convex inner or lingual 

 surface. They are latterly compressed to a slight extent, evenly 

 rounded in front, with their fore and aft diameter a little greater 

 than their breadth. The first or anterior tooth of the maxilla 

 is similar to the premaxillary teeth, in which respect Gorgosaurus 

 differs from other known genera of Cretaceous carnivorous 

 dinosaurs. The other maxillary teeth are long and powerful, 

 of the Megalosauroid type, with two serrated keels, one along 

 the front edge, the other behind. In the second maxillary tooth 

 the anterior keel in descending passes slightly toward the inner 

 side of the crown, and this is seen in a lessening degree in the 

 next two or three succeeding teeth. A similar slight variation is 

 seen also in the more anterior teeth of the dentary. 



The chevron bones are intervertebral, but with a greater 

 surface of attachment to the front vertebra of the two. The 

 more anterior ones are bent slightly backward from their mid- 

 length. This angulation in succeeding ones becomes more 

 pronounced until the lower edge of the distal half is parallel 

 to the longitudinal axis of the tail. By a gradually increased 

 development and prolongation forward of the anterior angula- 

 tion at the mid-length of the bone, a "meat-chopper" shape is 

 attained and adhered to with a gradual diminution in size, in ore 

 apparent in the depth of the bone than in the length of its 

 "foot." 



The long and slender anterior teeth (premaxillary and first 

 maxillary) of Gorgosaurus are very different in shape from the 

 robust supposed anterior teeth of Deinodon horridtis of Leidy. 

 In all the large Cretaceous carnivorous dinosaurs, the majority 

 of the teeth, apart from the more anterior ones, are remarkably 

 similar in the different genera and do not afford data for generic 

 distinctions. 



