FOSSIL TURTLES OF NORTH AMERICA. 



In case it shall hereafter be discovered that more than a single species is represented by 

 these bones, the lower jaw figured by Wieland shall be regarded as the type of L. wielandi. 



That this lower jaw is not identical specifically with that regarded as belonging to the 

 type of L. angusta appears from the following considerations: 



(1) The angle subtended by the cutting-borders of the jaw of L. angusta forms at least a 

 right angle; in L. wielandi this angle is 80 degrees. 



(2) In L. angusta the lateral outlines of the jaw continue outward and backward in nearly 

 straight lines to the mental foramina; in L. wielandi the borders are deflected more nearly 

 backward at a considerable distance in front of these foramina. 



(3) In L. angusta a line drawn from one foramen to the other falls 12 mm. in front of the 

 hinder end of the symphysis; in L. wielandi it falls at the hinder end of the symphysis. 



(4) In L. angusta the descent from the summit of the coronoid is much more abrupt than in 

 the other species considered. In the former species the height of the coronoid process is 77 

 per cent, of the length of the symphysis; in the new species, only 60 per cent. 



(5) The tip of the jaw of L. wielandi appears to have been more upturned, more acute, 

 and in every way more beak-like than in L. angusta. 



Differences so great as indicated above in two jaws whose symphyses are respectively 52 

 mm. and 42 mm. can hardly be attributed to differences in age or sex. At least, so great 

 differences do not appear in a number of jaws of the loggerhead turtle, to which the jaws of 

 Lytoloma have great resemblances. In a huge skull of the loggerhead, the length of which 

 from snout to occipital condyle is 230 mm., the line joining the mental foramina falls at the 

 hinder end of the symphysis, while it falls only 12 mm. behind the symphysis in a young 

 specimen whose skull is only 130 mm. long. As to the lateral outlines of jaws, the elevation of 

 the coronoids, and the form of the tip, there is not much difference among specimens of middle 

 and large sizes. The angle subtended by the outlines of the anterior portions of the lower 

 jaws of Caretta may, however, vary as much as in the case of L. angusta and L. wielandi. 



The width of the jaw forming the type of L. wielandi, taken at the mental foramina, is 

 66 mm.; taken at the hinder ends of the dentaries, 75 mm. The length of the symphysis is 

 42 mm. The greatest thickness at the symphysis is II mm. 



The front of the skull figured by Wieland agrees in size and in the angle made by the 

 borders of the upper jaws with the lower jaw just described. A comparison made with the 

 jaw of the loggerhead indicates that the skull of which it formed a part had a length of about 

 156 mm. Seen from above or below, it resembles considerably the same part in the log- 

 gerhead. Seen from the side, the tip of the snout is much more deprest than in the loggerhead, 

 a condition due probably to the little-developt cutting-edge of Lytoloma. Plate 28, fig. 7, rep- 

 resents Wieland's type skull seen from above; plate 28, fig. 8, as seen from below; and plate 

 29, fig. I, as seen from behind. These figures are reproduced from drawings made for Dr. 

 Baur in 1888. 



The orbit was large. The prefrontals joined along the midline for a distance of at least 

 12 mm. and to a line crossing the skull considerably behind the fronts of the orbits. In Rhe- 

 techelys platyops (Cope) the prefrontals were parted by the frontals to a line considerably in 

 front of the orbits. 



The external nasal opening has its transverse and its longitudinal dimensions each 20 mm. 

 The snout as seen from above is not acuminate, as it was in Rhetechelys platyops. 



The vomer appears, as in Rhetechelys platyops, to have wholly separated the horizontal 

 plates of the palatines. It has a length of 33 mm. and a width of 20 mm. The width of the 

 perpendicular plate of the vomer, between the narial passages, is 1 1 mm. The choanae are 

 thrown well backward, but it is doubtful whether they were pushed backward as far as they 

 were in R. platyops, to a line joining the hinder borders of the orbits. 



There is no certainty that the carapace described by Dr. Wieland belongs to the present 

 species, and it is so referred only because it seems to belong neither to L. angusta nor L. 

 jeanesi. 



This carapace (fig. 196) was received by Prof. O. C. Marsh, May I, 1869, it having been 

 sent to him from the upper greensand bed of the Cretaceous, near Barnesboro, New Jersey. 



The estimated length of the carapace is 580 mm.; the greatest breadth, 530 mm. In 

 general, it resembles the carapace of the loggerhead, but it is far less pointed behind, a con- 



