EMYDID&. 353 
The type of the species Emys petroler Leidy must be regarded as being the two epiplastrals 
figured by him in 1873. Leidy mentions and briefly describesia ‘nuchal bone and a hypo- 
plastral, but there is no certainty that these belonged to a member of the same species. The 
two epiplastrals are the right and the left, but they did not belong to the same individual. 
Dr. Leidy’s figures present a view of the lower surfaces; the figures here presented (plate 46, 
fig. 3) represent the upper surfaces. 
The individuals to which these epiplastrals belonged appear to have had plastra about 
200 mm. long, tho perhaps somewhat less. Dr. Leidy thought that the animal belonged 
to the genus “Trachemys and compared it especially with T. scripta (I. scabra). W hen 
compared with a specimen of the latter whose plastron is 270 mm. long da appear decided 
differences. 
The epiplastral lip of 7. petroler was 52 mm. wide; that of the specimen of 7. scripta 
referred to is 60 mm. wide, a difference due to difference of size of the individuals. The lip of 
T. petrolet is directed forward; that of T. scripta is rolled downward in front. The thickness 
of the epiplastrals of 7. petroler at the symphysis is 11.5 mm., somewhat more than that of the 
specimen of 7. scripta, altho the latter is so much larger. The backward extension of the lip, 
along the midline on the upper surface, is 29 mm. in 7. petroler; in T. scripta, only 23 mm. 
In the former the thickening referred to ends posteriorly much more abruptly than it Hoes in 
T. scripta. In both species it may be observed that the gular scutes overlapt the anterior ends 
of the entoplastron. There can be no doubt that 7. petroler is a species distinct from both T. 
scripta and T. elegans. The latter species occupies at present the region where 7. petrole: 
was found. T. ele -gans has a very different epiplastral lip, this being den concave above 
so as to resemble a spout; and not so thick. In both 7. scripta and T. elegans the gular sulci 
on the upper surface of the epiplastrals run outward and forward, while in T. petr lei they run 
directly forward. 
It will be observed from the figures that there are some differences between the two epi- 
plastra, but these are not sufficient to indicate distinct species. 
The nuchal bone (plate 46, fig. 4) mentioned by Dr. Leidy has a length of 46 mm. and a 
maximum breadth of 50 mm. The width at the free border has been 25mm. The border for 
articulation with the first peripheral is very concave. Where the sulci bounding the nuchal 
scute crost the free border there are very deep notches, so that the nuchal scute projects as a 
prominent tooth. The greatest thickness of the nuchal bone is 10 mm. 
The nuchal scute is 20 mm. long and 7 mm. wide at the base. The width of the scute on 
the under side of the bone is slightly be In T. scripta the scute is nearly twice as wide on 
the lower side as on the upper. In J. elegans the lower side is about one-half wider than the 
upper. The first vertebral scute of J. petroler has a width anteriorly of 27 mm., and it has 
grown wider posteriorly. In the specimen of J. scr:pta mentioned, the first vertebral is only 
18 mm. wide anteriorly. In the midline of the fossil nuchal there is a mere suggestion of the 
presence of a carina; in 7. scripta the carina is very distinct. As to the sculpture, there are 
faint ridges which occupy the same positions as the much more distinct ones in T. scripta and 
Te: desans: 
The hypoplastral bone mentioned by Dr. Leidy is present, as well as a second belonging 
to another individual. These are much thicker than the corresponding bones of 7. elegans 
and somewhat thicker than those of T. scripta. Here again we are uncertain whether these 
bones belong to the same species as the epiplastra. 
The nuchal bone above described resembles that of the species described by Cope under 
the name Pseudemys bisornatus, here called Trachemys bisornata. We must therefore consider 
the possibility that Cope’s species is identical with that described earlier by Leidy. This 
question can not be settled until additional materials have been collected at one or both of the 
localities, Hardin County and Atascosa County. 
Trachemys bisornata (Cope). 
Plate 56, fig. 1. 
Pseudemys bisornatus, Cope, Proc. Amer. Philos. Soc., xvi, 1878, p. 228. 
Trachemys btsornata, Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 449. 
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