142 FOSSIL TURTLES OF NORTH AMERICA. 
Wieland suggested that his type might prove to belong to O. erosus. However, the latter 
differs in having thicker bones and a longer nuchal. To illustrate this statement we will 
consider the seventh peripheral. The length of this is 88 mm., just three-fourths that of the 
same bone in the type of borealis, yet the thickness of the inner face is 47 mm.—7 mm. more 
than in the latter species. This is too great to be due to age or individual variation. The 
= length of the nuchal in borealis is go 
Width. mm. This bone is not present in the 
Peripheral. Length. Height. ecora a type of erosus, but the left peripheral 
ower face.|Upper face. s 
—— and first costal show that it extended 
backward at least go mm., and it cer- 
i 103 6o 23 i i Ks 
2 95 60 28 Bi me tainly was still longer. If the animal 
3 75 45 - 40 45 had grown to be a fifth or a fourth 
: oS <8 - ro ie larger the nuchal would have been 
6 104 68 : 60 50 much more than go mm. in length. 
7 te es = th ni) The anterior peripherals of O. erosus 
are higher than those of the type of 
borealis, altho the latter belonged to a considerably larger individual. 
On comparing the bones of borealis with those of Cope’s supposed sopitus in the 
American Museum of Natural History no important differences are observed. The nuchals 
agree. The surface of borealis is marked by pits resembling rain-drop impressions; but the 
surface of Cope’s specimen is so markt to some degree, and a larger specimen referred to the 
species has such impressions in abundance. Some differences do appear, when careful compari- 
sons are made among the measurements of the peripherals, but these fall within a few 
millimeters. Greater Oifeceners may be observed between other specimens which are regarded 
as belonging to O. borealis. Figures and measurements are presented above of various parts 
of Wieland’s specimen. A portion of these are taken from Dr. Wieland’s paper, but most 
of them have been kindly furnisht me by the author. 
Fig. 163 is redrawn from Wieland’s figure in the American Journal of Science and reduced 
by one-fourth making the figures one-eighth the size of nature. 
Fa 164a, 
Fics. 164-168.—Osteopygts borealis. Peripherals of type. 3. 
164. First left peripheral, with section (1642) of the 166. Anterior end of fifth peripheral. 
proximal end. In the section the upper surface 167. Anterior end of sixth peripheral. 
is directed toward the left. 168. Anterior end of seventh peripheral. 
165. Anterior end of third peripheral. 
Fig. 164 presents the first left peripheral from above, together with a view of the end 
which joins the nuchal bone; figs. 165, 166, 167, and 168 represent the anterior ends respect- 
ively of the third, fifth, sixth, and seventh right peripherals. 
The length of the first neural is 102 mm.; its greatest width is 55 mm. The first costal 
has a maximum width of about 120 mm. The second i is go mm. wide at the costo-vertebral 
sulcus. The first vertebral scute is about 285 mm. wide; the second, about 180 mm. 
The plastron (fig. 163) in general resembles that of O. gibbi; but the fontanels appear to 
have been larger and the bridge was wider. The latter has a width of 138 mm. The whole 
plastron had a width, taken across the hypoplastra, of about 520 mm. The hyoplastron 
extended forward from the hyohypoplastral suture 138 mm. 
