TESTUDO. 103 



mounds, which have been derived from the disintegration of the marly earths that 

 have sUd from above. The particular stratum in which they seem to have been 

 originally imbedded, is a pale flesh-colored, indurated, siliceous, marly limestone, 

 situated from thirty to forty feet above, as shown in Number 7 of the geological 

 section, page 13 of this memoir. In the succeeding pages I shall describe five 

 species of Tesiudo, but 'at the same time I suspect that they may not all be truly 

 distinct. 



Testudo IVebrascensis, Leidy. 



(Plate XIX.) 



Stylemys Nebrascensis, Leidy: Proc. Acad. Nat. Sci., 1851, v., 172. 



Tesiudo Nebrascensis, Leidy: Proc. Acad. Nat. Sci., 1852, vi., 59; Owen's Rep. of a Geol. Surv. of Wise, 

 etc., 567. 



Of this species I have the opportunity of examining four specimens from the 

 collections of Messrs. Culbertson, Captain Van Vliet, and Dr. Owen. All are more 

 or less broken, and two are crushed; all have lost the anterior and posterior mar- 

 ginal plates, and in one the carapace is almost entirely gone. They vary a little 

 in size, and apparently belonged to immature individuals, as the costal plates had 

 not yet been connected to the marginal plates by cartilage. 



The form of the species approaches very much that of the genus Ejnys, and is 

 more depressed than the Gopher, Testudo polyphemus. 



The marginal plates are oblique at the sides of the carapace, and turn abruptly 

 beneath at their lower third. 



The processes of the sternum, which act as columns of support to the carapace, 

 at the bottom of the lateral notches are remarkable for their prominence and thick- 

 ness. Those anterior are twenty-one lines long, four lines broad, and two and a 

 half lines thick, and ascend inwardly at an angle of about 45°, and are received at 

 their free extremity into a pit about the middle of the outer margin of the first 

 costal plate. Those posterior are equally strong with the former, and join the 

 carapace at the junction of the fifth and sixth costal plates. 



The sternum is flat, turned a little upward anteriorly, and is slightly convex at 

 its junction with the carapace. 



The axillary and inguinal notches are directed downward ; and the line of union 

 of the sternal with the marginal scutes is nearly parallel on the two sides. 



The species is the smallest and most depressed of those brought from Nebraska, 

 and in all the specimens the arrangement of the plates is the same, except in the 

 smallest, which has an additional vertebral plate introduced between the ordinary 

 eighth and the inverted V-shaped penultimate plate. 



Plates of the Carapace. — (PL XIX. Fig. 1.) The first vertebral plate has convex 

 sides, and in the smallest specimen, being the only one in which it is preserved, is 

 ten lines long and six broad. The vertebral plates, from the second to the eighth 

 inclusive, are hexahedral; and to the fifth are nearly equal in size, but afterwards 

 undergo a rather sudden reduction, and then also continue to be nearly equal. 



The second vertebral plate articulates with the first and second pairs of costal 



