THALASSEMYDID&. 143 
The humerus (fig. 163, hum) has an extreme length of 170 mm. The shaft dorso-ventrally 
is 17 mm. thick. The smooth rounded end is 54 mm. wide. The ulnar crest rises above the 
head. Between the plane of the two proximal processes the angle is obtuse. 
The pelvis (fig. 163 11, zsch, pub) resembles in general that of Chelydra. 
The specimen referred to above as having been described by Cope as Osteopygis sopitus 
is now in the American Museum of Natural History and has the number 2351. Tt consists 
of peripherals one to four, seven, eight, and ten, of the right side; peripherals one, three to 
five, seven, eight, and ten, of the left; the nuchal, the proximal portions of costals one to 
four of the left side; one nearly complete costal, perhaps the third of the right side; many 
fragments of other costals; a number of plastral bones; parts of both humeri; and a complete 
left femur. 
Cope has, from this specimen, produced a figured restoration of the carapace (Ext. Batr. 
Rept., etc., p. 139, fig. 39). This is represented as having ro pairs of costal plates and a corre- 
sponding number of neural bones. It is difficult to understand how that author could suppose 
that the rib of the first costal could extend far enough forward to enter the pit in the second 
peripheral. Evidently he saw no other possible use for the pit. The eleventh peripheral is 
not present. On the tenth is found the number “‘1o,” written in ink; but at that time the 
right hand digit ‘‘o’’ was written upon a “1.” Altho on page 235 of the work cited, Cope 
concluded that the genus Osteopygis had only nine pairs of costals, he maintained, from exami- 
nation of the present specimen, that Propleura had ten pairs. Nevertheless, in his Vertebrata 
of the Tertiary, publisht in 1884, he stated that Osteopygrs had 10 pairs and Propleura g pairs. 
Cope figured a part of the nuchal, 
Width. the first left peripheral, and a part of 
Peripheral.) Length. | Height. Thickness. the first left costal. They are refigured 
Lower face. Inner face. 
(hg. 169, p. 145), with the addition of 
fragments overlookt by Cope. The 
| 
| 
: 77 2 e - front of the carapace, along the nuchal, 
3 oa 42 39 font was somewhat concave. The free bor- 
4 73 36 29 40 ders of the nuchal and the anterior per- 
75 ea rt ie ipherals are obtuse and thick. At the 
7 2 65+ 57 24 midline the nuchal is 10 mm. thick. 
8 go - 16 . - The fore-and-aft length of the nuchal 
ne 87 88 aa - - is 78 mm.; its width along the free bor- 
der was close to 120 mm. The border 
which joined the first neural is only 5 
mm. thick. The table gives the dimensions of the peripherals, the measurements, except 
the lengths, being taken at the anterior ends. In a few cases a dimension has been taken 
from the contiguous end of the peripheral in front. 
The first peripheral was suturally joined to the first costal; probably also the second, but 
the border is missing. It is probable that all the other peripherals to the eleventh were free 
from the contiguous costals, but the upper border of the fifth has some appearance of having 
formed a suture. The upper faces of the anterior peripherals are nearly plane. Beginning with 
the fifth, the upper faces are more or less concave from the free edge to the costal border. The 
hinder peripherals have a thin acute border and this may be traced forward, but becoming less 
acute, to the first peripheral. In the hinder end of the second peripheral, in the inner face, is a 
pit, like a deep thumb impression, for the anterior prolongation of the hyoplastron. The other 
peripherals have each a pit for the end of the corresponding rib. They are at the middle of the 
length of the inner face. Most of them are circular in section, but those of the last two or three 
peripherals are somewhat flattened; and they notch the upper face of the bone. 
The first costal has a maximum width of 98 mm. The second is 66 mm. wide; the third, 
60 mm.; the fourth, 46 mm., all measured at the costo-vertebral sulcus. At the sutural 
borders these bones are 5 mm. thick. 
The surface of most of the bones is more or less roughened; and on many of them, espe- 
cially the costals, there are present scattered pits, each about 3 mm. in diameter. These pits 
are less conspicuous on the hinder peripherals. 
