44 



FOSSIL TURTLES OF NORTH AMERICA. 



are somewhat indefinite. There is no longitudinal ridge along the premaxillary symphysis; 

 hence the species is not a Gopherus, as defined by Agassiz under the name Xerobates. The 

 outer masticatory ridge is somewhat tootht; the inner ridge is rugose, especially posteriorly. 

 The latter nearly meet on the hinder borders of the premaxillae. The distance across the 

 pterygoids, where narrowest, is 18 mm. There are distinct ectopterygoid processes. The 

 outward border of each pterygoid is continued backward and outward as a sharp ridge to the 

 hinder part of the base of the quadrate. From the fore part of this base another sharp ridge 

 runs upward and inward mostly on the quadrate. Between the two ridges is found a rather 

 deep groove. 



The lower jaw (fig. 582) is complete. The depth varies from 22 mm. at the coronoid 

 process to 18 mm. at the symphysis. The masticatory surface is traverst lengthwise by a deep 

 groove; this does not join that of the opposite side at the symphysis. The external masti- 

 catory ridge is sharp and furnisht with small tooth-like processes. From these processes sharp 

 ridges run down on the outside of the jaw. The internal masticatory ridge rises higher than 

 the external. It is rough and dentated. Anteriorly these inner ridges are directed forward one 

 on each side of the symphysis and terminate in a blunt tooth where the outer ridges meet the 

 symphysis. 



den 



art 



FIGS. 581 AND 582. Testudo orthopygia. Skull of type, with lower jaw. X 

 581. Side view. 582. Lower jaw, upper view, art, articular; den, dentary; sur, surangular. 



Several of the dimensions of the plastron of this animal, as given by Cope, differ from those 

 obtained by the present writer. In the following table Cope's measurements are given in 

 parentheses, when differing from the author's: 



Millimeters. 



Length of plastron in midline 515 (615) 



Width of plastron at axilla 330 (360) 



Width at inguinal border 290 (310) 



Distance between posterior apices 100 



Millimeters. 



Width of base of anterior lip 132 (125) 



Width at end of anterior lip 70 



Length of anterior lip above 105 (100) 



Some of these discrepancies may be due to misprints, some perhaps to different methods 

 of taking measurements; but others appear to be obvious errors of determination. 



The plastron (plate 78, fig. i; text-fig. 583) is somewhat upturned at the front; also 

 moderately concave in the middle. Its length, given as 515 mm., is on a straight line from the 

 tip of the anterior lip to the bottom of the posterior notch. The apices of the posterior lobe 

 extend about 24 mm. further backward. The width of the plastron across the middle was 

 close to 450 mm. The greater portion of the free borders of the plastron is much thickened. 

 The figures indicate the form of the anterior lip. The width, 132 mm., is that taken between 

 the points where the sulci forming the outer boundaries of the gular scutes cross the free 

 border. Superiorly the lip runs backward some distance beyond this. Fig. 584 is a section 

 at what is here termed the base; and fig. 585, a section 25 mm. behind the end of the lip. 

 Fig. 586 is a longitudinal section of the lip in the midline. It shows to what extent the lip 

 is excavated posteriorly. 



The borders of the anterior lobe from the front to the axillae are acute. From the border 

 the bone thickens for nearly 50 mm., then thins toward the median portion of the plastron. 



