43 2 



FOSSIL TURTLES OF NORTH AMERICA. 



are the skull complete, the nearly complete shell, both shoulder-girdles, the left humerus, the 

 pelvis complete, 3 injured cervical and 4 caudal vertebrae, and a quantity of dermal bones. 



The individuals of this species appear to have reacht a large size, the length of the cara- 

 pace of the type being 922 mm. Their relationships were close to T . osborniana, as shown 

 both in the skull and the shell. 



The skull (figs. 566-568) lacks most of one of the posterior lateral angles. There has 

 occurred some crushing and distortion of the prefrontal region. The skull is slightly broader 

 in proportion to its length than in T. osborniana. In the latter species the width is 68 per cent, 

 of the length to the occipital condyle, while in T. impensa it is 72 per cent. This small differ- 

 ence may disappear on the examination of other specimens. The following are the principal 

 dimensions of the skull: 



Millimeters. 



Width of palatal fossa 39 



Length of the mandible 98 



Depth of mandible at the symphysis. ... 21 



The prefrontals meet along the midline 21 mm.; the frontals, 27 mm. The orbit is some- 

 what distorted, but its antero-posterior diameter is 34 mm. The width o'f the lugal arch appears 



566. 



FlGS. 566 AND 567. TestuJo impensa. Skull of type. X A- 

 566. Upper surface. C67. Palatal surface. 



to have been about 16 mm. The maxilla descends below the floor of the orbit 22 mm. The 

 cutting-edge, seen from the side, is convex in front, slightly concave posteriorly, but the con- 

 cavity seems to have been less than in T. osborniana, and the bone did not terminate posteriorly 

 in such a prominent process as in the latter named species. This cutting-edge is irregularly 

 dentated, especially in front. The antero-posterior extent of the otic region, measured across 

 the paroccipital and the prootic, is 31 mm., being contained in the length of the skull to the 

 occipital condyle 4.45 times. The lateral angles of the skull extend behind the occipital 

 condyle about 10 mm. In T. osborniana they extend but little beyond the condyle. The 

 portion of the skull in front of the postfrontals equals one-half of the length to the condyle. 

 In T . osborniana the portion mentioned equals only 0.45 of the length. 



The nasal opening has a width of 30 mm. The prefrontals lack 27 mm. of coming to a 

 perpendicular from the front of premaxilla?. In T. osborniana the prefrontals lack only 10 mm. 

 of reaching this perpendicular. 



