8^ 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. lesneuri 
examined contained only the l)ulbs of a sedge which Prof. 
T. J. Burrill thinks is almost certainly Ci/jjerus j^hymafo- 
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 In'ought together as serving for the separation of the 
two geographic turtles. 
M. lesueuri. — Head small, width contained al)oiit G.4 
times in length of carapace. Alveohu" 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 enlai-ged and 
thickened. Carapace wnth obscure median ridge ; dorsal out- 
line of central dorsal plates viewed from the side, a simple 
cinwe. Spot l)ehind 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, moUusks. 
