162 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXV. 



Dimensions of peripherals 



over the bridge. The dimensions of the peripherals are given in 

 the table. The pygal is 33 mm. from side to side and only 16 mm. 

 fore and aft. The neural bones have the usual forms and proportions. 

 This specimen shows distinctly that there were two large supra- 

 pygals, instead of one. as hitherto supposed by the writer. Plate 

 VI and fig. 17 of the writer's forthcoming Fossil Turtles of North 

 America show what was supposed to be a single suprapygal. The 

 figure on the plate referred to is, however, crossed by a white line, 

 which perhaps represents a suture, but which was taken to be a frac- 

 ture. The figure here presented shows the forms of the two bones. 

 The anterior measures 15 mm. on the midline; the posterior, 19 mm. 

 The greatest width of each is 50 mm. Baur a stated that there were 

 two suprapygals, but he did not describe them. From a figure pre- 

 pared for Baur and awaiting publication by the writer h it was sup- 

 posed that Baur had regarded the small bone succeeding the eighth 



neural as a suprapygal. Marsh represents 

 only a single suprapygal in the specimen 

 figured by him. 



On the inferior surface of the carapace 

 here described are seen the well-developed 

 heads of the ribs. The buttress of the 

 hypoplastron was strongly developed and 

 fitted into an excavation in the contig- 

 uous borders of the fifth and sixth costal bones. The buttress rose 

 about 18 mm. above the lower ends of these costals and was about 

 15 mm. thick fore and aft. Another specimen in the U. S. National 

 Museum. Cat. No. 5733, shows that there were similar axillary 

 buttresses/ 7 



The sulci between the A T arious dermal scutes are extremely narrow 

 and threadlike, but all are traced with little difficulty. That between 

 the second and the third vertebral scutes crosses, as usual in turtles, 

 on the third neural bone. The length of the third vertebral scute is 

 52 mm. ; of the fourth, 61 mm. ; of the fifth, 46 mm. The fourth has 

 a width of 72 mm. ; the fifth, a width of 60 mm. The marginal scutes 

 are mostly confined to the peripheral bones, rising to near the costo- 

 peripheral sutures. The eleventh pair, however, overlaps slightly 

 on the eighth costal and the twelfth on the hinder suprapygal. The 

 fifth vertebral extends backward to within 7 mm. of the hinder border 

 of the bygal. 



It is estimated that the carapace of this individual had a length 

 of 255 mm. 



a Proc. Acad. Nat. Sci. Phila., 1891, p. 411. 



6 Fossil Turtles of North America, p. 48, fig. 18. 



c Anier. Jour. Sci., XL, 1890, pi. vn. 



d Fossil Turtles of North America, pi. v, fig. 5. 



