TOXOCHELYID^:. 



177 



22 mm. wide, taken together. In T . latiremis, No. 1497 of the American Museum, with skull 

 only two-thirds as long as the type of T. procax, the interorbital space is 20 mm. and the ptery- 

 goids are 23 mm. T. procax is therefore characterized by a very narrow palate. 



The most important character for differentiating this species from T. latiremis is found in 

 the lower jaw. As shown by the symphyseal portions of the dentaries, the alveolar surface is very 

 broad, horizontal, and very slightly concave. In the midline this surface extends as far back- 

 ward as does the symphysis on the lower side of the jaw; whereas in T. latiremis the alveolar 

 surface extends backward little more than half as far as the lower face of the bone. 



From the type of Cope's T. serrifer this species is likewise distinguish! by the width of the 

 symphyseal portion of the alveolar surface. In T. serrifer the surface extends backward nearly 

 as far as does the lower surface of the bone; but the width above is contained in the length of the 

 alveolar surface nearly 5 times, whereas, in T. procax, it is contained only 2.5 or 3 times. The 

 inner face of the dentary is furthermore much deeper proportionally in T. serrifer than in 

 T. procax. From T. brachyrhina this species differs, so far as known, in having a more pointed 

 head and a still narrower pterygoid region. The lower jaws of the two can not yet be com- 

 pared. From T. stenopora the present species differs in a much wider narial orifice and in the 

 character of the lower jaw, as well as in various other respects. T. elkader has a relatively 

 broader skull and choanae not so far removed from the snout. The lower jaws of the two species 

 appear to be greatly alike. 



The length of the skull of the type of T. procax is 165 mm. from the tip of the snout to the 

 occipital condyle. The distance between the outer faces of the quadrates is 138 mm. Seen 

 from below the skull is wedge-shaped, and the snout rather pointed. The anterior narial 

 opening is of the usual form. Little can be said regarding the upper surface of the skull. 



The alveolar surface of the upper jaw (fig. 225) is broad, and a strongly developt and very 

 rough ridge starts from the premaxilla and runs backward, first on the premaxilla, then on the 

 palatine. Between the anterior ends of these ridges there runs a deep median groove. The 

 palatine bones encroach more on the choanae than they do in T. latiremis, so that these orifices 

 resemble somewhat those of Chelonia. The alveolar surfaces are fully as broad at the anterior 

 ends of the choanae as they are posteriorly; whereas in T '. latiremis they widen posteriorly. 

 There is a deep pit in the midline on the lower surface of the premaxillae, from which we may 

 infer that the lower jaw bore a sharp horny beak. The cutting-edges of the maxillae descend 

 but little below the level of the alveolar surfaces. 



The tympanic cavity appears to have had about the same degree of development that we 

 find in Caretta. 



At the symphysis (fig. 226) the alveolar, or masticatory surface, extends backward as far 

 as does the lower face of the bone, and each measures 32 mm. The alveolar surface is slightly 

 concave on each side of a low median ridge, which forks posteriorly. The symphysis has a 

 thickness of but 12 mm., which thinness may be due slightly to compression, but this is doubt- 

 ful. The groove on the inner face of the dentary continues to the symphysis. Fig. 227 repre- 

 sents another jaw fragment in the American Museum. Its number is 220. 



No. 2050 of the Kansas University furnishes the united dentaries of this species (fig. 228), 

 but it has belonged to a smaller specimen than the type. A small portion has been broken from 

 the tip. The total length of one dentary is 80 mm. The width of the masticatory surface at 

 the symphysis is 24 mm., and it extends as far backward as the symphysis does on the lower 

 side of the jaw. The thickness of the bone at the hinder end of the symphysis is 9 mm., but 

 in life this may have been greater. The masticatory surface is broad and flat, but narrows 

 posteriorly. Both the inner and the outer borders are sharp, the latter overhanging the groove 

 along the inner face of the bone. The groove just referred to passes forward to the symphysis. 



The writer has been enabled to examine a skull and lower jaw of this species, which belongs 

 to the University of Chicago. Its catalog number is 572. The exact locality in Kansas is 

 unknown. The skull is 117 mm. long from the snout to the condyle. The upper surface is 

 damaged to the same extent as in the type specimen. The masticatory surface of the lower 

 jaw extends backward 60 mm. from the tip of the jaw. Anteriorly it is somewhat concave, 

 but along the symphysis there is a rather prominent ridge. The thickness of the jaw at the 

 hinde'r end of the symphysis is 10 mm. 



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