138 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 whose length and breadth Professor Cope has given respectively as 2 inches 

 6 lines and I inch 9 lines. It was evidently suturally united with the first costal plate. 



The third peripheral (plate 28, figs. I, 2; text-fig. 154) of the right side is present. It has 

 an extent of 6 1 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 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 0. chelydrinus, yet he does not mention 

 the lower jaw in his reference of the species to Catapleura in 1875; but he does give, under 

 the genus Osteopygis, a description of the lower jaw, which description might have been based 

 on the jaw now under consideration; and no other jaw is known which has 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 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 "chelydrinus" 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 symphysis 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 fossae; 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, 5g. 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 Osteopygis erosus is now in the 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 



