TESTUDINID^E. 387 



This species is by far the most abundant fossil turtle found in any of the geological for- 

 mations in North America. Many years ago Dr. Leidy stated that he had seen hundreds of 

 the shells; and since that time many in addition have been collected and deposited in the 

 various museums. Some individuals attained a large size. Most of the specimens seen in 

 museums are of small or moderate size, for the large shells have not usually been regarded by 

 collectors as worth the trouble and expense of transporting. Statements made by reliable 

 collectors are to the effect that individuals are sometimes met with which have had a length of 

 3 feet (890 mm.) The type of Leidy's Testudo lata had a plastron 21 inches (about 530 mm.) 

 long. The largest shell in the American Museum of Natural History is 510 mm. long, 375 mm. 

 wide, and 265 mm. high. 



The species was described in early days by Leidy under several specific names, which are 

 mentioned in the synonymy. These so-called species were based in some cases on purely 

 individual characters; in others, on modifications of form due to distortion. Dr. Leidy him- 

 self was the first to correct these errors. The specimens from which were drawn the following 

 figures publisht by Leidy in vol. VI of the Smithsonian Contributions to Knowledge are in the 

 U. S. National Museum: Plate xix, figs. I, 2, 3 (Testudo nebrascensis); plate xx, figs. I, 2 

 (T. hemispherica); plate xxi, figs. I, 2 (T . oweni). The specimens from which were obtained 

 the figures of T. lata, op. cit., plate xxiii, plate xxiv, fig. I, are in the Philadelphia Academy. 



In form this tortoise was broad and rather high and vaulted. The height and convexity 

 appear to have increast with age. Often the rather low and flattened form is due to pressure 

 exerted during fossilization. Nevertheless, among specimens of the same size there are 

 differences in the form and height of the shell which must have existed during the life of the 

 animals. 



The width of the shell forms about 85 percent, of the total length. In outline the carapace 

 is truncated in front, or even a little concave; behind, it is broadly rounded. The peripherals 

 over the bridges are nearly or quite perpendicular; those over the limbs are slightly flared; 

 those in front slope downward and forward, or flare slightly upward; the pygal is nearly 

 perpendicular. The free edges of the anterior and posterior peripherals, the nuchal, and the 

 pygal are acute. The neurals, excepting the first, which is oval, are almost always hexagonal, 

 with the two shortest sides directed forward. Occasionally, as in the type of Leidy's T. 

 culbertsoni, the second neural is octagonal, the third quadrangular (Ancient Fauna Neb., 

 plate xxii, fig. i). There are usually 2 suprapygals, the larger anterior of which is bifurcated, 

 as in Testudo; the smaller posterior one is rhombic, with its lower border fitting in a notch in the 

 upper border of the pygal. In Leidy's type just referred to there is an accessory plate in front 

 of the first suprapygal; and the same condition is occasionally met with in other specimens. 



The costal plates are modified somewhat as they are in the genus Testudo. The second, 

 fourth, and sixth are somewhat widened distally and narrowed proximally, while the third 

 and fifth are narrowed at the distal end and widened at the proximal. The degree of this 

 differentiation varies somewhat with individuals, and in general is not so much developt as in 

 S. conspecta and S. capax. In uncrusht examples of the species the bridge peripherals rise 

 nearly half the height of the shell. In a specimen whose length of carapace is 260 mm. the 

 height of these peripherals is 58 mm. The suture between the costals and the peripherals is a 

 very loose one, as in Testudo. 



The sulci bounding the carapacial scutes are narrow, but rather deeply imprest. The 

 nuchal scute is very narrow. The first vertebral is wider by one-half than the second. The 

 fourth is somewhat narrower than the second and the third; while the fifth is nearly as wide 

 as the first. On the bridge peripherals the sulci run obliquely downward and forward. The 

 sulci between the costal scutes and the marginals follow closely the sutures between the 

 costal and peripheral bones. On the hinder pygal the sulcus runs slightly above the suture. 



The anterior lip of the plastron projects little, if any, beyond the general curve of the 

 anterior lobe. The outline of the lip is rounded or repand, and the edge is rather acute. 

 Superiorly the lip thickens backward for a distance about equal to the width of a gular scute, 

 and then ceases abruptly, but there is no excavation behind it. The entoplastron is narrow 

 in front and broad behind. The width of the bridges is not quite one-half the length of the 

 plastron. The lobes are so wide that space is left only for the movement of the limbs and for 

 the tail. There is a notch in the hinder border of the plastron, and the apices of the xiphi- 



