TESTUniNID^E. 



433 



The root ot the mouth (fig. 567) resembles closely that of T. osbormana. The outer ridge 

 of the masticatory surface is strongly developt and dentated. Anteriorly it continues forward 

 on the premaxilla of its side; so that between the right and left ridges there is, in the pre- 

 maxillary region, a deep furrow. The inner ridge of the masticatory surface is broad and 

 rough behind and divided by a deep longitudinal groove. The palate is deeply excavated. On 

 each pterygoid there is a hookt ectopterygoid process. The distance across the two pterygoids 

 is 30 mm. 



The lower jaw (figs. 568, 569) is large and heavy. Its length from the symphysis to the 

 angle is 98 mm.; its height at the coronoid process, 32 mm.; at the symphysis, 21 mm. Each 

 ramus has its masticatory surface divided longitudinally by a deep groove. From the outer 

 cutting-edge sharp ridges run down on the outer face of the dentary. 



The total length of the shell is 922 mm.; the width, 725 mm. The height can not be 

 exactly determined, on account of injuries to the carapace (plate 76). The middle region of 

 this has been broken in, and the fragments considerably disturbed, while the unbroken portions 

 of the costals and to some extent, the peripherals, have been somewhat deprest. It appears. 



FlGS. 568 and 569. Tcstudo impensa. Skull and lower jaw of type. X^. 

 568. Skull, right side. 569. Lower jaw, seen from above. 



The 



s 7 i 



however, improbable that the shell ever had as great height as that of T. osbormana. 

 width of the carapace is 78 per cent, of the length; whereas, in T. osbormana the width 

 per cent. The peripherals have practically the same form as in the last-mentioned species, 

 but those of the bridge regions do not appear to have had relatively as great height. Neither 

 do the peripherals of the posterior region descend so steeply as in T. osbormana. In the latter 

 the pygal and the adjoining peripherals slope forward from the perpendicular only about 15 

 or 20; whereas, in T. impensa the forward slope is about 45 . A part of this angle is due 

 possibly to depression, but this seems improbable. The anterior outline of the carapace is 

 convex not straight or concave as in T. osbormana; and the anterior border does not pass so 

 abruptly into the lateral border. 



On account of the crushing in of the upper part ot the carapace, it has been difficult to 

 determine the dimensions of the neurals, but the following statements may be relied on. The 

 first neural (fig. 570) is oval in form, and the width has been close to 70 mm. The second is 

 octagonal, and had a width, where greatest, of 120 mm. The third is hexagonal, y^ mm. 

 long and 97 mm. wide. The fourth is octagonal, 76 mm. long, 112 mm. wide. The sixth is 

 hexagonal, 70 mm. long and 100 mm. wide. The seventh is 63 mm. long and 1 18 mm. wide. 



The third and the fifth costals are expanded at their proximal ends and each is in con- 

 tact with three neurals. 



The pygal is 145 mm. wide at its upper end, 1 14 mm. at the tree border. The first supra- 

 pygal has the usual bifurcate form and is in extensive contact with the pygal and the eleventh 

 peripherals. The second suprapygal is 90 mm. long and 84 mm. wide. 



The plastron (plate jy, text-fig. 571 ) has a total length of 805 mm. The width, from tin 

 outer border of the hyoplastron of one side to that ot the other, is 650 mm. There is a con- 

 siderable concavity in the region between the inguinal notches. The width of the anterior 

 28 



