396 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



but little thickened, and they pass gradually into the common surface 

 of the plastron. The inferior surface exhibits a delicate grooving, 

 wbich is parallel to the long axis of the animal; it is most distinct just 

 behind the dermal cross-sutures. This species is about the size of the 

 Pseudemys elcgans. The typical specimen is adult. 



Measurements. 



M. 



Lcugth of plastron minus clavicles (episternals) 0.165 



Length of posterior lobe 0.075 



Width of posterior lobe at base 0.090 



Length of a vertebral bone 0.020 



Width of the same 0.018 



Length of a costal bone 0.019 



Thickness of the same 0.0025 



Length of anal marginal (lateral) 0.025 



Width of anal marginal 0.022 



Length of first marginal behind bridge 0.020 



Width of first marginal behind bridge 0.029 



This species differs from the P. klegans in the absence of the median 

 emarginations of the posterior marginal bones ; in the absence of notch 

 of the posterior lobe of the plastron at the end of the anal suture ; and 

 in the general absence of ridges on the costal bones. The median 

 notch of the anal marginal bone is more pronounced in the existing 

 species. 



This tortoise was discovered by Eussell S. Hill, to whom it is dedi- 

 cated- 



