128 FOSSIL TURTLES OF NORTH AMERICA. 
When this author’s work (Synopsis of the Extinct Batrachia, Reptilia, and Aves of North 
America) was issued in 1870, he described (pp. 105-234) both Osteopygis and Propleura 
as possessing 10 pairs of costal plates. In the latter genus he included only the species 
sopitus, his repandus being made the type of a new genus Catapleura, and his chelydrinus 
being referred to Osteopygis. Cope concluded that there were 10 pairs of costals because he 
found a pit, as if for a rib, in the second peripherals and supposed that he had found a pit in 
each of the eleventh peripherals. 
In that portion of the Synopsis (pp. 235-252) which appeared in December, 1870, Cope 
stated that as regards Osteopygis the ascription to it of 10 pair of costals was an error, the last 
peripheral not having had a costal corresponding to it. As to Propleura, he adhered to his 
previous opinion ark it possest 10 pairs of costals. 
In 1875 Cope (Vert. Cret. Form. West, p. 257) had concluded that the possession by Pro- 
pleura sopita of 10 pairs of costals was very doubtful; and this species, with platylomus and 
his new erosus were referred to Osteopygis; while chelydrinus went to Catapleura. Cope 
still believed that Osteopygis possest at least g pairs of costals. 
In 1882 (Proc. Amer. Philos. Soc., xx, p. 144) and again in 1884 (Vert. Tert. Form. 
West, p. 112), Cope defined Osteopygis as having 10 pairs of costals and Propleura as having 
g, statements directly opposite to those formerly made. 
The correction of Cope’s errors regarding the number of costals in the species of this group 
was made by Dr. Baur (Zool. Anzeiger, x1v, 1889, p. 42). He studied the very complete 
specimen which has since served Dr. Wieland as the type of O. gibbr; and from this he 
concluded that there were only 8 pairs of costals, and that the pit in the second peripheral 
was for the reception of a process of the hyoplastron. Baur examined also Cope’s types of 
the species of Osteopygis, Propleura, and Catapleura and concluded that there were no generic 
differences among them. 
Baur’s results respecting the number of costals have been confirmed by Wieland. Never- 
theless, Wieland adopts Cope’s genus Propleura. He holds that Propleura differs in having 
costo-peripheral fontanels, conical rib-pits, and humeri grooved on their distal ends. 
So far as concerns the grooving of the distal articular ends of the humeri, the present 
writer does not believe that enough is known about the humeni, not only of the species of the 
group in question but of the living species, to justify the use of the character proposed by 
Wieland to separate genera. Among species of Testudo it is found that the distal end of the 
humerus of many, perhaps of most, is smooth and rounded; but that of Testudo orthopygia 
has a broad trochlear groove. 
ANALYSIS OF THE SPECIES OF OsTEOPYGIS. 
1. All the peripherals sutured to the costals (Osteopygis). 
A. Posterior peripherals emarginate; upper borders of peripherals not notcht by the 
rib pits; thickness of outer end of nuchal about one-eighth its width. emarginatus 
AA. Posterior peripherals not emarginate. 
a. Outer end of nuchal about one-eighth the width in front; upper borders of 
peripherals notcht by rib-pits . : gibbt 
aa. Thickness of outer end of nuchal about one-sixth its width in iron upper 
borders of peripherals not notcht by rib-pits. ae ae robustus 
2. Peripherals 3 to ro inclusive free from the peripherals (Propleura). 
A. Hinder peripherals angulated at end of sulcus ; : chelydrinus 
AA. Hinder peripherals neither angulated nor emarginate. 
a. Rib-pits of eighth and succeeding peripherals flattened; one face or both notcht 
by rib-pits. The seventh at least two-thirds as wide as long. 
. Bones thick and heavy; thickness of distal end of first peripheral in its length 
3.5 times; only upper face of hinder peripherals notcht by rib-pits. . erosus 
bb. Boucs thinner, thickness of distal end of first peripheral in its (enech 
4.4 times; both faces of upper border of hinder peripherals notcht by 
FIDE PLES! visor dis <b <n die epel syseePaya- aca ved sts ee aecrenrape eRe agence le ah memes : borealis 
bbb. Bones thinner; thickness of fist peripheral i in its s length 4.4 times; rib-pits 
of sixth and seventh peripherals flattened; both faces of peripherals notcht p/atylomus 
aa. Seventh peripheral only half as wide as long Res ere sopitus 
