THALASSEMYDIDJE. 153 



The pygal bone (figs. 189, 190) had a width of about 80 mm. along the free border. Some 

 of the upper border has crumbled away, but the height of the bone was close to 65 mm. Its 

 thickness a short distance below the upper border is 19 mm. The upper surface is concave fore 

 and aft; convex from side to side. On the lower side the directions of these forms of surface 

 are reverst. The free border is acute. The upper border was probably suturally articulated 

 with the suprapygal. On neither the upper nor the lower side of this bone is there any trace 

 of a sulcus. 



Of the eleventh peripheral Cope had no more than is now present, the hinder half, articu- 

 lated with the pygal. It is concave from the free edge to the upper border on the upper surface, 

 rather strongly convex on the lower surface. In the upper border there remains a portion of 

 the deep pit for the rib-head of the eighth costal. The greatest thickness of the bone is 1 9 mm. 

 While a considerable part of the free border is broken away, that remaining seems to indicate 

 that this border was emarginate, as was stated by Cope. No sulcus appears on this bone. 



Two of the costals represented are evidently those of the same pair. Cope thought they 

 were those of the second pair. The proximal end was 82 mm. wide. One of the sutural 

 borders is 1 1 mm. thick, and the suture is oblique to the surfaces of the bone. It was evidently 

 overlapt by the bone to which it was articulated. The opposite border is only 5 mm. thick. 

 Under C. repanda reasons have been given for regarding the border bearing the oblique suture 

 as the anterior one; and the costals of the two species are so similar that the same rule applies 

 here. As in C. repanda, the rib-head is strongly developt, as well as the rib in its course along 



190 



FIGS. 189 AND 190. Catapleura ponderosa. Portions of type. X. 

 189. Pygal and eleventh peripheral. 190. Section along midline of pygal. 



the under side of the costal. As in C. repanda, this rib gets nearer and nearer the thickened 

 side of the costal on its way toward the distal end. There is also a rough groove near the prox- 

 imal end of the front of the ridge; but it is not so conspicuous as in the other species. More- 

 over, it is seen only on the two costals supposed to belong to the second pair. 



On none of the costals or peripherals are there observed any remains of sulci, to mark the 

 limits of the horny scutes. The costals are markt by very distinct branching vascular grooves. 



There is present a fragment of a plastral bone, which was interpreted by Cope as the 

 hinder part of the left hypoplastron. The writer finds it impossible to identify the bone satis- 

 factorily. One border is obtuse and 14 mm. thick. The opposite border is thin and irregular. 



Only the proximal half of the right humerus is present. The long axis of the head 

 measures 35 mm., the shorter 24 mm. The radial process is missing, but it continued to the 

 head of the bone. The ulnar process lacks much of rising to the level of the head, and the ridge 

 descending from it runs well down on the shaft. The planes of the radial and ulnar processes 

 make with each other an angle of more than 90. The shaft of the bone is comprest having 

 a diameter of 15 mm. in the perpendicular plane ; of 1 1 mm. in the horizontal, 

 comprest in a manner directly opposite to that of the Chelonnda;. 



The femur is that of the right side and lacks the distal end. The portion remaining is 93 

 mm. long; and the whole bone must have been about 120 mm. long. As in the more primitive 

 turtles, the head and the processes resemble those of the humerus. The head has dumet. 

 respectively of 23 mm. and 30 mm. 



