88 FOSSIL TURTLES OF NORTH AMERICA. 
the intercostal sutures are a few of the grooves described by Cope. Fortunately the sutures 
between the bones are yet open, so that the whole structure can be observed. The most 
striking feature of the carapace is the presence of two bones in the region usually occupied by 
the nuchal,asmall anterior and a large posterior. The anterior bone (fig. 76,nu.p), here regarded 
as the true nuchal, has awidth of 52 mm. and a length, fore and aft, of 30mm. The other bone, 
the preneural (fig. 76, pren), is 75 mm. wide and 38 mm. long. The first neural is pyriform, 
the others hexagonal, with the wider end forward. 
The first three peripheral bones are each 42 mm. high. 
Those over the bridges have a height of about 65 mm. 
Neurals. Vertebrals. 3 fy ae > 
There are 6, instead of 5, vertebral scutes, the areas usually 
No. a 5 Set 2 : 
covered bythe first being transversely divided. The dimensions 
Length, Width. Length. Width. of the neurals and vertebrals are shown in the table. 
The nuchal scute is small and was probably not divided 
1 44 42 40 70 along the midline. It is 24 mm. wide and 10 mm. fore and 
Z 57 ch 2 i|p C2 aft. The first marginal is small and triangular. The second 
3 60 39 111 115 fe 5 5 : 
Fi ee 30 «0s, | aig | has a length of 25 mm. along the free border and a height of 16 
5 48 38 of mm. The third is not so high. Those marginals over the 
6 : 34 
bridge rise above the borders of the costal bones and have 
a height of approximately 70 mm. 
A little of the hinder border of the plastron (fig. 77) is broken away, but the total length 
was very close to 415 mm. In general it resembles the plastron of species of Baéna. The length 
of the anterior lobe is 113 mm.; its width at the base, 160 mm.; at the outer ends of the gulo- 
humeral sulci, 85 mm. The entoplastron is 65 mm. long and 45 mm. wide. The symphysis of 
SO the epiplastra is only 14 mm. long. From 
x 
pe the entoplastron the hyoepiplastral sutures 
ee run outward and backward. The bridge 
4 has a width of 180 mm. The mesoplastra 
{ join at the midline for a distance of 20 mm., 
( the left one being somewhat the wider. 
They expand outward to awidth of 105mm. 
The length of the hinder lobe was 
originally about 105 mm. Its basal width is 
175 mm.; at the hypoxiphiplastral suture, 
145 mm.; at the femoro-anal sulci, 120 
mm. The thickness of the center of the 
anterior lobe is 11 mm. Between the 
axillary buttresses, on the upper surface, 
runs a broad ridge which thickens the bone 
to 15mm. A similar ridge crosses from 
one inguinal buttress to the other. From 
C3 ale the latter buttresses a ridge runs backward 
BiG: 77.—Chisternon hebratcum. Plastron. » i. No. near each free border of the hinderlobe, and 
5961 A. M. N. H. Shows bones and scute areas. thru these the thickness is 17 mm. The 
central part of the hinder lobe is concave. 
The skull (plate 21, figs. 3, 4; plate 23, fig. 1; text-fgs. 78-81) of this specimen is nearly 
complete, lacking only a part of the left maxilla, and the premaxilla. At the time the writer 
publisht his figures of this skull, he had not yet discovered the differences between this 
specimen and that numbered 5962, described here as Chisternon undatum. In order to allow 
comparisons the measurements of the two skulls are given in the table on p. 89. 
There is a difference of only 5 mm. in the lengths of the skulls. There is a difference of this 
same amount in the widths of the maxilla below the orbits, a difference of 8 mm. in the widths 
of the skulls at the quadrates, a difference of 6.5 mm. in the distances from the orbit to the 
tympanic cavity. 
The skull is short, broad behind, wedge-shaped in front. The temporal region is broadly 
rooft over and the squamosal comes into contact with the parietal. 
