142 



Hay Batrachians and Reptiles of D. C. 



subcaudals, 19 to 25. Ground color above, cream color to yellowish or 

 very dark brown, with three rows of confluent irregular brown spots 

 forming zigzag cross blotches, bordered with sulphur yellow; tail black; 

 upper lip sulphur yellow; lower lip lighter; belly yellow with some 

 mottlings and sprinklings of black. Length, 2 to 5 feet. 



The evidence as to the occurrence of the rattlesnake within our limits 

 is not altogether satisfactory, yet it is of such a character as to make it 

 seem extremely probable that the species is still to be found about the 

 rock slides along the Potomac River above the city. 



Key to the species of Chelonia. 



\ 



a. Tail long, about equal to the plastron. - Chelydra serpentina, 49. 

 aa. Tail much shorter than the plastron. 



b. Marginal plates, 22. 



c. Hinder lobe of plastron considerably more than as wide as the 



carapace. - - - - Kinosternon pennsylvanicum, 50 

 cc. Hinder lobe of plastron not more than as wide as the carapace. 



Aromochelys odwata, 51. 

 bb. Marginal plates, 24. 



d. Plastron without hinge, immovably joined to the carapace. 

 e. Plates of carapace nearly or quite smooth. 



/. Carapace without round yellow spots. 

 g. Neural and costal plates alternate. 



Pseudemys rubriventris, 52. 



gg. Neural and costal plates arranged in 4 nearly straight rows 

 across the back. _-- : ;.',*. . Chrysemys picta, 53. 

 ff. Carapace with many round yellow spots. 



Ckmmys guttatus, 54. 



ee. Plates of carapace rough, each one with low, concentric ridges. 



Malaclemmys centrata, 55. 



dd. Plastron with a hinge across its middle and united by a movable 

 suture with the carapace. - - Terrapene Carolina, 56. 



FIG. 3. Topography of a turtle, e, nuchal plate; n, neural plates; co, 

 costal plates; m, marginal plates; g, gular plates; h, humeral plates; pe, 

 pectoral plates; ab, abdominal plates; /, femoral plates; an, anal plates; 

 c, carapace; p, plastron; al, alveolar surface; t, tongue. 



