82 THE DIFFERENCES BETWEEN 



Previous to examining the alimentary contents I had ob- 

 served a worn appearance of the alveolar surfaces and 

 numerous shining particles in- the crevices, the meaning of 

 which was now explained. 



The digestive tubes of most of the adult M. lesueuri 

 examined contained only the bulbs of a sedge which Prof. 

 T. J. Burrill thinks is almost certainly Cyperus phymalo- 

 des. In some cases this species was found to have eaten 

 cray-fish. Holbrook says it feeds on small fishes, rep- 

 tiles, etc. 



SUMMARY OF DIFFERENCES. 



From the preceding matter the following characters may 

 be brought together as serving for the separation of the 

 two geographic turtles. 



M. lesueuri. Head small, width contained about 6.4 

 times in length of carapace. Alveolar surfaces of jaws 

 not greatly expanded. Supra-occipital spine small, not 

 thickened. Median ridges of carapace prominent; the 

 dorsal outline of central dorsal plates concave before the 

 tubercles. A comma-shaped yellow spot behind each eye, 

 frequently continued posteriorly as a stripe on the neck. 

 A yellow spot on the symphysis of the mandible. Averag- 

 ing smaller than the following. Food mixed, animal and 

 vegetable. 



M. geographicus. Head large, width contained about 

 4.6 times in length of carapace. Alveolar surfaces of jaws 

 greatly expanded. Supra-occipital spine enlarged and 

 thickened. Carapace with obscure median ridge ; dorsal out- 

 line of central dorsal plates viewed from the side, a simple 

 curve. Spot behind eye isolated, not comma-shaped, di- 

 rected longitudinally. A stripe on symphysis of mandible. 

 A stripe originating on tympanum. Larger than the pre- 

 ceding. Food, mollusks. 



