IJ C 



1-OSSIL TURTLES OF NORTH AMERICA. 



by Cope, " 10 R," but the digit on the right had evidently been changed from " I " to "o" and 

 an "L" to an "R." Finally ink lines had been drawn across these characters and "8" 

 written near by. These changes indicate that originally Cope regarded the peripheral as the 

 eleventh; that before he went into print he came to regard the bone as the tenth; and 

 that at some later period he became convinct that it was the eighth. The measurements 

 of the bone do not at all agree with those of the tenth peripheral of Cope's first specimen, 

 but the)' do agree quite closely with those of the tenth ot the second. 



Cope (his plate vii, fig. 3a) has represented the nuchal, the right first peripheral, and the 

 proximal end of both first costals. These elements are here shown in fig. 134. The free 

 border of the nuchal and first peripherals is obtuse. At the midline, back from the free 

 border, the thickness is 15 mm. The free border of the nuchal is 122 mm. long, in a straight 

 line. The first peripheral is 65 mm. along the free border, and 48 mm. at right angles with 

 this. It is 17 mm. thick at the proximal end (fig. 135) and 19 mm. at the distal (fig. 136). 

 The upper surface is convex, with a low concavity running parallel with and just behind the 

 free border. 



The fifth left peripheral (Cope, pi. vii, fig. 3^, seen from the lower and inner faces) 

 measures 77 rrjm. along the free border; 58 mm. on the upper face anteriorly, 60 mm. poste- 

 riorly; 52 mm. across the inner face anteriorly, 48 mm. posteriorly. The inner face contains 

 a large pit, circular in section, for the end of the rib of the third costal. This pit occupies 

 about one-third the length of the peripheral. The upper face is concave up and down; the 

 lower lace is convex. There was no sutural connection with the plastron, but the upper 

 border of the upper face was suturally joined to the costal. Fig. 137 represents the anterior 

 end of this bone; 138 the posterior end. The hinder end of the bone corresponds exactly with 

 the anterior end of the sixth peripheral of O. erosus. 



i.W- 



Figs. 135-141. Osteopygis emarginatus. Portions of shell 



135. Section of proximal end of first left peripheral. 



136. Section of distal end of first left peripheral. 



137. Anterior end of fifth left peripheral. 



138. Posterior end of fifth left peripheral. 



T4- 141. 



i No. 1485 A. M. N. H. 



139. Anterior end of eighth left peripheral. 



140. Hinder end of eighth left peripheral. 



141. Neurals. 



The eighth peripheral (Cope, plate vii, fig. 3c) is nearly plane above. The free border is 

 mostly missing, hut it had apparently about the form shown restored in Cope's figure. It 

 was therefore rather strongly emarginated, the bottom of the emargination being at the end of 

 the sulcus. The fore-and-aft extent of the bone at the middle of the height is 90 mm.; the 

 height from the end of the sulcus, too mm. It must have been about 1 15 mm. high at the ends 

 of the bone. The greatest thickness at the anterior border (fig. 139) is 24 mm.; on the 

 posterior border (fig. 140), 22 mm. On the upper border the bone was sutured to the costal 

 touching it. The rib-pit, mostly in the posterior half of the inner face, is 30 mm. long and is 

 flat. It does not notch the upper face. 



The first costals (fig. 134) present only their proximal halves. The greatest width fore 

 and aft is 97 mm. The thickness in front is 12 mm.; posteriorly, 8 mm. The rib-head was 

 prominent. In front of the ridge descending from it is a rough surface to which was articulated 

 the rudimentary first rib. 



Among other fragments of costals is the distal two-thirds of one, probably the fourth. It 

 is possibly the one mentioned by Cope as having a width of 3 inches and 2 lines, this being the 



