139 



FAMILY IV. EMYDID^. THE POND TURTLES. 



The Fourth aud last Family of Tint Ir.s round in this Slate in 

 eludes eleven ditTei-«'nt species, and is (•((nse(inen(ly by far the 

 largest. They are calh'il I'ond Turth's not Ix'cause they are found 

 exclusively in ponds, but because they are most common in such 

 places. They are to be re<-o<^nized by the (\V(d\(' plates compi'isinj; 

 the plastron or under- shcdl. the carapace oi- upper part of the shell 

 beinj;; hij^her at alxuit the middle, its edge flaring outward, and the 

 lower jaw without a long point at the union or tips. As with the 

 Box Turtles, the tail is short and without a crest, and the plastron 

 is broad. Also the claws are mostly five in front and four behind. 

 Generally the lobes of the plastron are not hinged, but sometimes 

 the anti'rioi' lobe moves on a transverse hinge, and rarely the pos- 

 terior lobe can be so moved, thus enabling the animal to completely 

 close the shell. 



About eighty species of I'ond Turtles are known, of which eleven 

 are found or may reasonably be expected within the borders of 

 I'ennsylvania. These belong to seven Genera, which are distin- 

 guished by the following analytic key: 



Key to Families and Species of Emydidae or Pond Turtles. 



(A) No hinged piece in plastron or lower shell. 



(B) Alveolar or crushing surface of jaws broad; carapace low; 

 toes short, broadly webbed. 



(C) Crushing surface of jaws smooth with a deep groove in front; 

 upper jaw not notched in front; head covered with soft skin; cara- 

 pace more or less keeled. 



(D) Lower jaw with a spoon-shaped dilation at tip. Genus 

 Graptemys (Agassiz). 



(E) Middle series of plates on back scarcely overlapping. Sp. 7. 

 Graptemys geographicus. Map Turtle. 



(EE) Middle series of plates on back distinctly overlapping. Sp. 

 8. Graptemys pseudogeographicus. False Map Turtle. 



(DD) Lower jaw without spoon-shaped dilation at tip. Genus 

 Malaclemmys; Sp. 9. Malaclemmys centrata. Diamond-back. 



(CC) Crushing surface of upper jaw divided by a longitudinal 

 ridge paralled with margin; upper jaw notched in front (in all but 

 species 11); head with thin hard skin; carapace scarcely keeled. 

 Genus Pseudeinys. 



(E) Jaws coarsely toothed. Sp. 10. Pseudemys rubriventris. 

 Red-bellied Terrapin. 



(EE) Jaws not toothed or serrated. Sp. II. Pseudemys hiero- 

 glyphica. Hieroglyphic Turtle. 



(BB) Crushing surface of jaws narrow. 



