78 GEOLOGICAL SURVEY OF TEXAS. 



within the edge it is much thickened and displays three surfaces. These 

 are: first, a flat level extending to the border; second, a flat face look- 

 ing downwards; and third, the concavity forming the superior wall of 

 the thoracic cavity. Surfaces everywhere smooth. 



, Measurements of No. 1. 



Mm. 



Diameters Of plastron j anteroposterior 365 



( transverse 310 



Diameters of anterior lobe of plastron \ anteroposterior 89 



( tranverse 186 



Diameters of posterior lobe of plastron -j anteroposterior 110 



( transverse 240 



Width of posterior notch of plastron 70 



Depth of posterior notch of plastron 25 



Length of epiplastron (diagonal) 87 



Width of lip (total) at base 90 



Length of lip on middle line above 40 



Thickness of lip at fundus of thoracic cavitj' 27 



Diameters of inferior aspect of mesoplastron . J anteroposterior .58 



( transverse 80 



Distance between humero-pectoral and pectoro-abdominal scutal suture on 



middle line 25 



The lip of the plastron is not produced and bifurcate, as in T. agassizii 

 (from S. E. California), but the posterior lobe is quite similar to that of 

 the latter species. The posterior lobe of the T. laticaudata is inter- 

 mediate in proportions between those of T. hexagonata and T. poly- 

 phemus. Both of the extinct species may belong to the genus Xerobates, 

 Ag., but this can not be determined until the crania are discovered. 



The specimens of this species are smaller than the single one which 

 represents the T. laticaudata. Though allied to the latter, the forms of 

 the lobes of the plastron display too many differences to permit me to 

 regard them as identical. 



Rock Creek; W. F. Cummins. 



EDENTATA. 

 MYLODON, Owen. 



MYLODON PSODALIS, CopC. 



Bulletin U. S. Geological Survey Terrs., 1878, p. 385. 



The distal part of a femur, lacking part of the internal condyle and 

 adjacent epicondyle, represents a gigantic species of Mylodon. At pres- 

 ent it is not possible to determine exactly its specific relations, but its 

 association with the species of the Equus fauna renders it possible that it 

 is the animal which has been found associated with the same fauna in 

 Oregon, and which 1 have named as above. The measurements of the 



