100 FOSSIL TURTLES OF NORTH AMERICA. 
The piece of epiplastron present is g mm. thick. The gulo-humeral sulcus crosses the 
hinder end as in Gly ptops and Baéna. 
The length of the hyoplastron, from the epiplastral suture to the mesoplastron, is 120 mm. 
The width of the anterior lobe was about 142 mm. The distance from the axillary notch to 
the mesoplastron measured yery close to 50mm. ‘The thickness of the bone at the entoplastral 
suture is 6mm. The free border in front of the axillary notch is subacute. Most of the border 
which rose to meet the peripherals is broken away. A portion of the sulcus between the 
abdominal scute and the anterior inframarginal is present. 
The length of the hypoplastral at the midline is go mm.; the width at the base of the 
hinder lobe, 80 mm.; the width from the midline to the union with the bridge peripherals, 
130 mm. A portion of the outer end of the bone is missing, but a section of the sulcus is seen 
starting forward from the inguinal notch and section of another sulcus between the hinder 
inframarginal and the contiguous marginals. The hinder inframarginal has a width of about 
45mm. Its anterior end appears to have extended on the mesoplastron. 
The fragment of xiphiplastral is 53 mm. long. It shows the free border. This is subacute, 
and from it the bone thickens soon to 10 mm. No portion of the upper surface was covered 
with scutes. On the lower surface the femoro-anal sulcus crost the bone about 30 mm. behind 
the suture with the hypoplastron. The form of the hinder border of the lobe can not be 
determined. 
Of the skull there is present the pedicel of the left quadrate. The condyle for the lower 
jaw is concave, 11 mm. from side to side, and less than 5 mm. antero-posteriorly. At the inner 
side of this condyle there ascends toward the lower end of the parietal plate a sharp ridge. The 
rough surface for the pterygoid lacks 8 mm. of reaching the condyle, a fact that enone that 
hit genus did not belong to the Pleurodira. 
The upper surface of the carapace was more or less uneven, especially along the midline. 
All the articular borders of the bones are striated perpendicularly to the sutures. Besides this, 
there is a delicate pitting of the surface which gives the effect of leather. The lower halves 
of the costals are markt by coarse ridges, which have been produced during the growth of the 
costal scutes. 
The plastral bones have all the sutures conspicuously markt by striz, which run at right 
angles with the sutures. The whole surface is occupied by a fine network of delicate ince 
Genus POLYTHORAX Cope. 
An insufficiently known genus of uncertain position. Plastron suturally united with the 
carapace; furnisht with the usual scutes, besides intergulars and interhumerals. Lower jaw 
with narrow ramus; the triturating surface bounded outwardly by a sharp margin; the 
symphysis short. 
Type: Polythorax missuriens1s Cope. 
This genus is arranged provisionally among the Baénida; but it is probable that it and 
Archeochelys Lydekker belong to a distinct family. 
Polythorax missuriensis Cope. 
Polythorax mussurirensts, Cope, Proc. Acad. Nat. Sci. Phila. 1876, p. 258; Bull. U. S. Geol. and Geog. 
Surv. Terrs., 111, 1877, p. 573.—Hay, Bibliog. and Cat. Foss. Vert. N. A., 1902, < 438.—HatTcHER, 
Bull. U. S. Geol. Surv. 257, 1905, p. 77. 
It is not at present known what has become of the type of this species. It was found in the 
Judith River deposits of Montana, in 1876. The plastron appears to have been pretty complete, 
but we are not told how much of the carapace was secured. No part of the species has ever 
been figured. 
The plastron had a total length of 183 mm.; hence the individual was not a large one, 
perhaps attaining about the size of our Trachemys elegans. The anterior lobe had a length of 
49 mm. The bridge was 76 mm. wide and as long. ‘The anterior lobe is stated to have been 
narrower at the base than the bridge. We must eoreline therefore that this lobe was not one- 
third as wide as the carapace. Its anterior extremity was rounded. The width of the base of 
