IOWA ACADEMY OF SCIENCE 153 



CHELYDRIDAE. 



Under surface of tail with large shields. 



Cheilydra, ScJiweig. 



Three moderately high keels on carapace. 



(Chelydra serpentina L.) 



Under surface of tail with scales. 



MACROCHEiLYS. 



Three very high keels on the carapace; turtles of large size. 



(Macrochelys lacertina.) 



CINOSTERNIDAE. 



Plastron very narrow, not protecting the fleshy parts. 



Armochelys. 



Two distinct yellow lateral stripes on head. 



(Armochelys odoratus Latr.) 



Plastron wider, protecting the fleshy parts when lobes are closed. 



CiNOSTERNUM. 



Plastron moderate; head spotted; carapace speckled. 



(Cinosternum pennsylvanicum Bosc.) 



EMYDIDAE. 



Plastron without hinge; immovably fixed to carapace. 



Alveolar surface of jaws broad; carapace more or less distinctly keeled. 



Malacoclemys, (gray). 



Alveolar surface of jaws narrow; carapace never keeled. 



ChRYSEM YS. ( GRAY^ ) . 



Plastron with a transverse hinge; toes scarcely welsbed.. , 



ClSTUDO. 



MALACOCLEMYS (gray). 



Keel moderately developed; not rising in form of tubercles; a network of fine 

 yellow lines on carapace. 



M. geographicus Lesueur 



Keel rising in form of tubercles in a high serrate series; no such fine yellow 

 lines on carapace. 



M. lesueurii (Gray). 



CHEYSEMYS (Gray). 



Carapace perfectly smooth, not keeled; not serrate at hind margin; bright red 

 markings on marginal shields, especially below. 

 Plastron immaculate, yellow. 



C. picta Hern. 



