TESTUDO. 103 
mounds, which have been derived from the disintegration of the marly earths that 
have slid 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 Zestudo, but at the same time I suspect that they may not all be truly 
distinct. 
Testudo Nebrascensis, Lervy. 
(PLate XIX.) 
Stylemys Nebrascensis, Leidy: Proc. Acad. Nat. Sci., 1851, v., 172. 
Testudo Nebrascensis, Leidy: Proc. Acad. Nat. Sci., 1852, vi., 59; Owen’s Rep. of a Geol. Sury. of Wisc., 
ete., 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 mys, and is 
more depressed than the Gopher, Zestudo 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. XTX. 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 
