242 Illinois State Laboratory of Natural History. 



showing above as a very narrow marginal spot. Posterior 

 margins of legs and edges of webs of the feet yellow. 



Length of shell, 4.50, width, 3.19; depth, 2. 



Occurs in streams and lakes throughout the State. Deep 

 Lake, Lake Co.; Chicago: Peoria (Brendel); Pekin; Little Fox 

 River at Phillipstown; Running Lake, in Union Co.; Southern 

 111., common (Butler). 



Few of our turtles change more with age than this. The 

 carapace in young examples is sharply keeled and the posterior 

 margins of the plates are elevated, giving an appearance of 

 imbrication; the nuchal plate is square or transverse, while the 

 marginals are nearly or quite as wide as they are long. In old 

 examples there is no trace of a dorsal keel or appearance of 

 imbrication. This is a small but strong and irritable species 

 which occurs in considerable numbers in muddy lakes and 

 rivers. 



Family OHELYDRID-ffl. 



Shell bony, covered with horny plates. Plastron small, 

 cross-shaped, with ten, nine, eight, or fewer, plates. Inguinals 

 present or wanting. Head large, jaws naked. Digits 5-4, the 

 two median longest; fully webbed. 



With two rows of marginal plates on each side. Head with 

 symmetrical plates. Tail without dorsal crest. 



Mackoclemts. 



With one row of marginal plates for each side. Plates of 

 head small and indistinct. Tail with a dorsal series of 

 elevated plates forming a crest Chelydea. 



Maoroolemys, Gray. 



Gray, Cat. Shield Rept., 1885, p. 48. 



Cope [Macrochelys] Proc. Acad. Nat. Sci. Phila., 1872, p. 23. 



Carapace with a wide channel on each side of the middle 

 line, with two rows of marginal plates. Plastron small; bridges 

 narrow, each covered by an elongate plate within, and without 

 by the contiguous axillary and inguinal. Head very large, 

 with symmetrically disposed plates above. 



