TKSTUDINIDA). 



431 



from the free border to the notch being only 83 mm. The thickness of the border which articu- 

 lated with the eleventh peripheral is 30 mm. The exterior surface of the bone is rather strongly- 

 convex both from side to side and from above downward. The inferior surface is concave 

 from side to side, convex from above downward. The free border is acute. In fig. 564 the 

 inferior or inner surface is that toward the left hand. 



The portion of the posterior suprapygal remaining indicates that the width of this bone 

 was about 60 mm. It is 20 mm. thick. 



The eleventh peripheral (figs. 563, 565) is narrow above, widening below. The height is 

 98 mm.; the width of the upper border, 45 mm.; that of the free border, 87 mm. The exterior 

 surface next the pygal is nearly plane; that near the tenth peripheral strongly concave up and 

 down, the free border here being considerably flared upward. Fig. 565 is a view of the end of 

 the bone which joined the tenth peripheral. The greatest thickness is 31 mm. About 37 mm. 

 below the upper border of the bone the thickness is rather suddenly reduced, forming a shoulder 

 on the inner side of the bone. The upper border is only 13 mm. thick. 



It is necessary to compare these bones with the corresponding ones of various other species 

 of Testudo. 



They resemble most the pygal and the eleventh peripheral of T . impensa. The dimen- 

 sions of the pygal of the latter species are as follows: Height, 145 mm.; width above, 146 mm.; 

 width along the free border, 90 mm. It will be seen that, relatively to the height, the width is 

 greater. The exterior surface, too, is less convex in all directions. The eleventh peripheral of 

 T . impensa measures as follows: Height, 122 mm.; width above, 80 mm.; at the free border, 

 123 mm. 



T. osborniana, type, has the pygal I IO mm. high; 113 mm. wide above; 80 mm. wide on 

 free border. It will be observed that the lower border is relatively considerably wider. The 

 outer surface is likewise considerably less convex than that of T . arenivaga. The eleventh 

 peripheral of T. osborniana has a height of 105 mm.; a width of 66 mm. along the upper 

 border; and a width of 106 mm. along the free border. The two bones have therefore quite 

 different proportions. 



The pygal of T. pansa is of a different form, being wider below than above, and not so high 

 as wide. 



T. undata has the hinder peripherals more strongly flared upward than are those of the 

 present species. According to Cope the pygal, too, is flared upward toward the free edge. 



Especially is it to be compared with T. edce of the same beds. The type of the latter is a 

 much smaller individual. The table presents measurements of parts common to the two species. 



It will be observed that the width of the pygal of T. arenivaga is less compared with the 

 height than in the case of T '. edce. Again, the eleventh peripheral of T. arenivaga is consid- 

 erably broader in comparison with the pygal than is the case with these bones in T. edce. 

 The differences in the proportions of the bones of the two species is well brought out by 

 making plots with the measurements given, those of T. arenivaga being divided by 2. 



Testudo impensa sp. nov. 



Plates 76, 77; text-figs. 566-571. 



The dry-land tortoise to which the above name has been given was discovered by Mr. 

 Albert Thomson, of the American Museum of Natural History, in 1902, in the Loup Fork 

 Miocene deposits of Montana, a short distance above the mouth of the Madison River. The 

 locality is in Broadwater County. The number of the specimen is 5867. The parts represented 



