35^ FOSSIL TURTLES OF NORTH AMERICA. 



Genus GRAPTEMYS Agassiz. 



Shell moderately elevated, with dorsal keel more or less strongly developt. Neural plates 

 hexagonal, with broad ends in front. Hinder border ot carapace serrated. Inguinal buttresses 

 rather feeble, articulated to the fifth costals. Humero-pectoral sulcus crossing behind the 

 entoplastron. Plastron with a median notch behind. Alveolar surfaces of the upper and the 

 lower jaws broad, flat, and smooth. Alveolar plate of the vomer in contact with the palatines. 

 Choanae between the hinder borders of the orbits. Symphysis of lower jaw long, equal to 

 half of the distance between the quadrates. 



The type of this genus is G. geographica, the geographic terrapin of the Mississippi 

 Valley (figs, i, 2, shell). This genus is distinguisht from Chrysemys, Pseudemys, and Trach- 

 emys by its maxillary and dentary alveolar surfaces, which are broad, flat, and without longitu- 

 dinal ridges. From Maldclemys it differs in having broader alveolar surfaces, and especially 

 in having the vomer in contact with the palatines on the alveolar surfaces. This articulation 

 and the broad, flat crushing-surfaces of the jaws remind us strongly of the condition found in 

 Lytoloma, as well as in the Toxochelyidae and the Cheloniidae; and show us that similar 

 structures may arise independently in different groups. The evident purpose of these broad 

 jaws in Graptemys is the crushing of hard food substances. G. geographica lives habitually 

 on mollusks. The relations of the palatines and the vomer need further study. 



There can be little doubt that Graptemys has been derived from Malaclemys. 



Von Reinach described (Abhandl. Senckenb. Gesellsch., xxvm, 1900, p. 92, plate xxx, 

 fig. 1 ) a new genus and species {Promalococlemmys boulengeri) believed to be closely related 

 to Malaclemys. There can be hardly a doubt that what is represented in his figure as the 

 hinder end of the plastron is in reality the anterior end of another specimen. 



Graptemys? inornata (Loomis). 



F 'g s - 455. 45 6 - 

 Chrysemys inornata, Loomis, Amer. Jour. Sci. (4), xvm, 1 904, p. 429, figs. 10, I I. 



This species is based on a nearly complete shell which was discovered by Dr. F. B. Loomis 

 in the year 1903, in the Titanotherium beds of the White River deposits, in Spring Draw 

 Basin, 10 miles east of Creston, Meade County, South Dakota. The specimen lay beneath 

 the skull of a titanothere; but, as no other skeletal parts of the turtle were found, the shell 

 had probably drifted thither. Through the liberality of Dr. Loomis I have been enabled to 

 study the specimen. 



In outline the shell is broadly oval, broadly rounded in front, and rather pointed behind. 

 The elevation of the shell in life can not be determined, it having been crusht flat during 



burial. The length ot the carapace (fig. 455) is 303 mm.; 

 the greatest width, 253 mm. Its margin is slightly excavated 

 in front, with shallow notches at the outer ends of the pos- 

 terior marginal sulci, and with a notch in the border of the 

 pygal. There appears to have been a rounded carina on the 

 front of the carapace, and this reappears near the rear. 



The nuchal bone has a length of 53 mm. and a width 

 of 66 mm. The eighth neural is followed by 2 suprapygals. 

 The accompanying table presents the dimensions of the 

 median bones behind the nuchal. 



The borders of the carapace in front of and behind the 

 bridges are acute and the bones are thin. The second per- 

 ipheral bone has a width of 38 mm. at right angles to the 

 margin of the shell; the ninth, a width of 40 mm. The sulci 

 between the marginal and the costal scutes run along on the peripheral bones a short distance 

 below the costo-peripheral sutures, except in front, where they deviate further from the sutures. 

 Posteriorly the sulcus crosses the midline on the rear of the second suprapygal. The nuchal 

 scute is 14 mm. long and 15 mm. wide. 



The vertebral scutes are narrow. Each of the anterior four is about 50 mm. wide. The 

 fifth has an extreme width of 70 mm. 



