352 FOSSIL TURTLES OF NORTH AMERICA. 



length of the bone is 6 1 mm. The front border is excavated slightly; the hinder border widely, 

 for the reception of the first neural. The length along the midline is 47 mm. The width ot the 

 anterior border is 37 mm.; the greatest width, 80 mm. The anterior border is acute. From 

 this the bone thickens backward on the under side a distance of 47 mm., where, at the mid- 

 line, it is 20 mm., at the border for first peripheral, 25 mm. ; then it thins rapidly to the hinder 

 border, where it is 13 mm. at the midline, 10 mm. at the sides of the notch for first neural. 



In this species the front of the first neural is on a line with the lateral angles of the bone, 

 an unusually forward position. The neural must have been of uncommon width, not less than 

 50 mm., occupying thus five-eighths of the width of the nuchal. This first neural must, too, 

 have been 13 mm. thick in front. 



The nuchal scute is 34 mm. long, 6 mm. wide in front, 12 mm. wide posteriorly. On the 

 inner side of the bone it extended backward 21 mm. The first marginal had an extreme fore- 

 and-aft extent of 40 mm. The front of the first vertebral scute is 41 mm. wide. It extended 

 forward on the nuchal only 13 mm. at the midline. The lateral angles of the bone are occupied 

 by portions of the first costal scutes. 



The upper surface of the bone is beautifully sculptured with grooves and sharp, inter- 

 rupted ridges. On the nuchal scute area the ridges run parallel with the midline. On the 

 areas of the first marginal scutes the ridges are short and suddenly interrupted at their anterior 

 ends. They run forward and outward, making an angle of about 25 with the midline. The 

 ridges on the front of the first vertebral scute area are short, almost tubercular, and are parallel 

 with the midline. On the areas of the first costal scutes the ridges are coarser and they run 

 outward and backward, making an angle of 64 with the midline. 



No other parts are known that can be referred with certainty to this species. No neurals 

 in the collection are broad enough to belong to it. A peripheral (plate 54, fig. 11), the right 

 eighth, appears to be worthy of reference here on account of its sculpture and thickness. It 

 has a height of 50 mm., a width of 39 mm. below, and of 33 mm. above. The free border is 

 acute. From this the bone thickens rapidly, so that near the middle of the height it is 26 mm. 

 where it joined the sixth peripheral; 19 mm. where it articulated with the ninth. On the inside 

 of the bone, at the upper posterior angle, is a pit for the end of a rib, probably the sixth. On 

 the articular face for union with the fifth peripheral there is a striated depression, which appears 

 to have been a part of a pit between the two peripherals for a rib, the fifth. On the same face, 

 nearer the inner surface of the bone, is a rounded smooth depression which indicates that the 

 sternal chamber reacht this face. Still nearer the inner surface of the bone is an excavation 

 apparently for a part of the inguinal buttress. 



The sculpture of this bone resembles that of the nuchal ot Derrochelys flortdana. How- 

 ever, the thickness appears to be too great for the latter species. 



A left third costal in the collection is referred provisionally to this species (plate 54, fig. 

 12). It presents the proximal end. The width, just outside the costo-vertebral sulcus, is 38 

 mm. It belonged to an individual with a carapace about 340 mm. long. The most conspicuous 

 character is the great thickness at the suture with the neurals, this being 20 mm. The thick- 

 ness diminishes to the costo-vertebral sulcus where it is 9 mm. The thickening has produced 

 a broad keel along the back. The sculpture agrees well with that of the type nuchal bone. 



Trachemys petrolei (Leidy). 

 Plate 46, figs. 3, 4. 



Emys petrolei, Leidy, Proc. Acad. Nat. Sci. Phila. 1868, p. 176; Contrib. Ext. Vert. Fauna West. Terrs., 

 1875, pp. 260, 340, plate ix, fig. 7. Cope, Ext. Bat., Rept., and Aves N. A., 1869, p. 128. Hay, 

 Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 448. 



Dr. Joseph Leidy states in his original description of this species that the types had been 

 submitted to him for examination by Messrs. George N. Lawrence and D. G. Elliot, of New 

 ^ ork, and that they had been previously presented to the New York Lyceum of Natural 

 History by Mr. Robertson. The specimens were reported to have been obtained from blue 

 clay and sand beneath a bed of bitumen, in Hardin County, Texas. The age is Pleistocene. 

 These bones and most of those accompanying them are impregnated with bitumen. They 

 now belong to the American Museum of Natural History and have the catalog number 3933. 



