256 FOSSIL TURTLES OF NORTH AMERICA. 
hypoplastron a distance of 14 mm.; while the right hypoplastron comes into contact with the 
left xiphiplastron. ‘The greatest thickness of the hyoplastron and hypoplastron is 18 mm. 
The distance between the entoplastron and the xiphiplastron is 84 mm. Half of this may be 
regarded as belonging to the hyoplastrals; the other half to the hypoplastron, 
The bridge is 100 mm. wide. The hinder lobe is much reduced. The width at the base 
is about 68 mm.; its length, 48 mm. The greatest thickness of the xiphiplastra is 16 mm. 
The plastral scutes are well exhibited. Leaving out of count the inframarginals, there 
are 5 pairs of plastral scutes, instead of the 7 that we find in ddocus. One pair occupies the 
area covered in 4docus by the intergulars, the gulars, and the humerals. This pair joins along 
the midline a distance of 23 mm. The members of the pair differ somewhat in size and form. 
Behind this pair the median sulcus is erratic in its course. The pectorals measure 48 mm. 
along the midline; the abdominals, 31 mm.; the femorals, 38 mm.; the anals, 28 mm. Here, 
as in 4. tardus, there appear to be only two inframarginals on each bridge, a small axillary 
scute and a very large scute behind this, reaching to the inguinal notch. Sonic of the marginal 
scutes descend on fie outer ends of the plastral bones. 
As stated, the eleventh and twelfth marginal scutes rise above the superior borders of the 
peripherals supporting them. In front of them the marginals are confined to the peripherals. 
Agomphus oxysternum (Cope). 
Fig. 320. 
Amphiemys oxysternum, Corr, Proc. Amer. Philos. Soc. xvi, 1877, p. 82; Palaontolog. Bull. No. 25, 
1877, p. 2; Amer. Naturalist, x11, 1878, p. 129. 
A gomphus oxysternum, Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, p. 445-—WIELAND, Amer. Jour. 
Sci. (4), XX, 1905, p- 443. 
The type of the present species is in the collection of the Geological Survey of Georgia, at 
Atlanta, where the writer has been permitted to study it. The specimen was found near Monte- 
zuma, Macon County, near the Flint River, in what is known 
as the Midway formation, a member of the Lower Eocene. It 
is in the same condition as when it was described by Professor 
Cope, the plastron being present, as well as the anterior portion 
of the carapace and the left border as far as the hinder end of the 
eighth peripheral. The core of matrix which filled the shell is in 
large part present and on it are indicated the sutures between the 
series of neural and costal bones. In form the shell appears to 
have been similar to that of 4. tardus. 
The length of the carapace, from the front of the nuchal to the 
hinder border of the seventh costal, is 242 mm. Cope gives this as 
250mm. The width is 184 mm.; the height, 150 mm. or a little 
more. 
The free border in front of the bridge is thick, obtuse, and 
slightly flared upward. The hinder end of the eighth peripheral 
is 18 mm. thick, and the free border is very obtuse. The nuchal 
bone measures about 50 mm. along the free border, 75 mm. 
where widest, and 41 mm. from front to the rear. The neurals, 
except the first, are slightly wider than long. The dimensions of 
three of them are given in the table on the “following page. 
The neurals and costals are thick. Cope states that the 
second neural is 13 mm. thick; the second costal, 12 mm. The 
Fic _ latter bone near the neural is only 10 mm. a The first per- 
IG. 320. —A gomphus ox yster- 28 | hr d 
poe (Cape ane ipheral measures along the free border 38 mm.; the third, 40 
x}. mm. The first is 33 mm. high; the second, 38 mm. 
The first vertebral scute is 53 mm. long and 52 mm. wide. 
Its lateral borders are nearly parallel. The second vertebral is 70 mm. ode The marginal 
scutes, as far backward as the middle of the bridge, run about is mm. below the costo-periph- 
eral sutures. 
