GEOLOGY AND PALEONTOLOGY. 197 
the middle portion of the right side has been restored from the left. In shape 
the carapace is broad and but little pointed posteriorly. As preserved it is but 
slightly convex, though doubtless more so in life. The surface is smooth, except 
where marked by the shield grooves. It differs from other American Cretaceous 
turtles of allied structure in the almost complete ossification. Except in the 
first pleural, there is between each and the peripheral a small, rounded or oval 
vacuity, with smooth, rounded, thickened margins. The margins, however, are 
so closely pressed down upon the peripherals that their precise nature is not 
easily made out. 
The neurals are narrow throughout; they are smooth, without protuberance 
or elevation, and they show no trace for attachment to the vertebrae below. The 
second, third, and fourth, all that are preserved anteriorly, articulate on the 
anterior lateral margin angularly with the preceding pleurals, behind which the 
lateral borders are nearly straight and parallel. The last neural and a part of 
the one preceding it are preserved; they are narrower than the anterior ones. 
There are two post neurals; the first is large and triangular in shape, with the 
anterior apex truncated for the eighth neural. The second is of about the same 
size as the first, and in the shape of a regular trapezium, articulating broadly 
behind with the pygal. 
The pleurals are of the usual number—eight. The first is relatively small, 
joining in its full length the first and second peripherals, and by its apex the 
third; the second pleural is, perhaps, the broadest of all, and joins the third, 
the whole of the fourth, and a small part of the fifth peripherals; the third 
pleural, nearly as broad, joins the most of the fifth and a small portion of the 
sixth peripherals; the fourth pleural, also broad, joins the most of the sixth and 
more than half of seventh; the fifth pleural, the narrowest, especially proximally, 
joins a part of the seventh and more than half of the eighth peripherals; the 
sixth pleural, a little broader than the fifth, joins for about an equal extent the 
eighth and ninth peripherals; the seventh pleural has the larger part of its distal 
border joined to the ninth peripheral and a lesser portion to the tenth; the eighth 
pleural articulates almost exclusively with the tenth, just touching the eleventh. 
The peripherals, of the usual number, are narrow anteriorly, broad and massive 
posteriorly. On the posterior part, near the middle of each bone, where the 
shield suture reaches the thin margin, there is a marked angulation, with the 
intervening borders concave; these angularities are slight or none at all anteriorly. 
The nuchal bone is, unfortunately, largely missing, so that it is now impossible 
to say whether or not there was an articulation with the cervical vertebrz so 
characteristic of the sea turtles. The pygal is small; its borders are thin and 
placed at an obtuse angle with each other, and with a semicircular notch in the 
middle, where they meet. 
The shields are well indicated by grooves, and are of the usual number and 
arrangement, as in Chelone or Chelydra. The vertebrals are relatively small. 
The cervical and caudal are of considerable size. The first lateral is relatively 
small. There are four laterals. The pygal shield is double, making twenty-five 
as the entire number. 
Of the plastron, the hyoplastron and xiphiplastron are complete or nearly so; 
the hypoplastron lacks the outer part on both sides; and of the epiplastron, only 
a small part, suturally united to the hyoplastron, is preserved. In the drawing, 
the elements of the two sides are separated as far as the carapace would permit. 
In all probability, if not certainty, however, the bones of the two sides inter- 
lock in the middle, leaving only a median fontanel, of moderate size, and a 
slender one between the xiphiplastra. 
