128 FOSSIL TURTLES OF NORTH AMERICA. 
The second peripheral of the left side (plate 23, figs. 6, 7; text-fig. 153) measures 64 mm. 
along the free border and has a minimum width of 45 mm. From the thin costal border the 
bone thickens rapidly on the lower side until a thickness of 16 mm. is attained at the proximal 
end of the bone and of 19 mm. at the distal end. The inner half of the lower surface is a little 
concave; the outer half very convex and rising to meet the upper surface. The anterior half 
of this face looks forward. The distal end oF the lower surface is deeply excavated for the 
outer anterior angle of the hyoplastron. There can be little doubt, it is believed, that this is 
the peripheral w hose length and breadth Professor Cope has given respectively as 2 inches 
6 lines and 1 inch g lines. It was evidently suturally united with che first costal plate. 
The third peripheral (plate 28, figs. 1, 2; text-fig. 154) of the right side is present. It has 
an extent of 61 mm. along the free margin and 42 mm. at right angles with this. It presents 
three faces, an upper, an inner, and a lower. The inner face is concave and is to a great extent 
occupied by an excavation for the reception of the rib of the first costal plate. Its width is 42 
mm. where widest. It is separated from the lower face by a sharp ridge. 
The upper face is nearly plane except in front where it rises to the summit of a ridge, 
on which it joins the lower face. A sulcus crosses this face nearer the proximal end. Its hinder 
border is grooved by the sulcus between the marginal and the first costal scute. The maximum 
width of this face is 34 mm. The lower face is quite convex vertically, the upper portion of it 
looking upward and forward, the remainder downward and forward. Its width is 23 mm. 
What distinguishes these anterior peripherals especially is the carina where the upper face 
meets the lower. 
Accompanying the bones above described is the lower jaw of a turtle, consisting of the 
united dentaries (plate 28, figs. 3, 4). This has written on it, doubtless by Professor Cope, the 
name “‘chelydrinus.”” It is hardly conceivable that he would not have mentioned this j jaw had 
it been present when he described the other bones. It is difficult to understand why he should 
have referred it to this genus and species without some good reason, when it would naturally 
have been placed in his genus Lytoloma. It is possible that he discovered after his description 
had been publisht that it belonged with the type of O. chelydrimus, yet he does not mention 
the lower jaw in his reference oe the species to Catapleura 1 in 1875; but he does give, under 
the genus Osteopygis, a description of the lower jaw, which description might have heen based 
on the j jaw now under consideration; and no other jaw is known which ae been referred to 
Osteopygis. The matrix clinging to the jaw is exactly like that on the peripherals. The 
matter is very obscure. 
This jaw resembles that of Lytoloma angusta, but there are at least specific differences. 
Figures of it are here presented. In the j jaw called“ “chelydrinus” the outline is almost that of 
a semicircle whose center lies a little behind the posterior end of the symphysis and whose 
radius is 38 mm. In Lytoloma angusta the outlines of the jaw run in nearly direct lines from 
the front of the masseteric fossa to near the tip of the jaw. In the jaw “‘chely ‘drinus”’ a line 
joining the mental foramen, lying in the front of the left masseteric fossa, with that of the 
right side falls at or a little behind the posterior end of the symphysis. In the type of Lyto- 
loma angusta the same line falls in front of this end of the symphy sis a distance equal to 
one-sixth the whole length of the symphysis. In “‘chelydrinus” the symphysis forms 47 per 
cent. of the width of the jaws at the front of the masseteric fossa; in Lytoloma, 58 per cent. 
It is quite evident, therefore, that the jaw labeled ‘“‘chelydrinus” represents a species distinct 
from Lytoloma angusta. It differs fully as much from the jaw figured by Wieland under the 
name Lytoloma angusta, here described as Lytoloma wielandi. 
Osteopygis erosus Cope. 
Plate 26, fig. 2; text-figs. 155-162. 
Osteopygis erosus, Cope, Vert. Cret. Form. West, 1875, p. 258.—Hay, Bibliog. and Cat. Foss. Vert. N.A., 
1902, p. 441. 
The type of Cope’s Osteopygrs erosus is now in ie American Museum of Natural History 
and bears the number 1130. The specimen appears to have been discovered in the upper bed 
of Cretaceous greensand, at Barnesboro, New Jersey, in 1869. It was probably found too 
late for inclusion in the monograph of 1869 and was reserved for publication until 1875. The 
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