124 



nym of (leographica, as well as the plain language of his descriptions. It 

 may be a very objectionable name, but the laws of priority must be rigidly 

 observed. 



The masticatory surfaces of M. g(0(jraphica are much broader than those 

 of M. pxeudogeogra phica, and we might infer therefrom that the food of the 

 two species is not the same. In \'olume XXII of the Bulletins of the Es- 

 sex Institute, Prof. Harry Garman has made the observation that the broad 

 surfaces of M. (jcograpJiiat are employed in crushing the shells of molluske, 

 the remains of which he found in their stomachs. In the stomachs of 

 M. psrndogeographicd, on the other hand, he found the remains of a species of 

 sedge, as well some animal matter. During the month of May, 1891, at a 

 meeting of the Indiana Academy of Sciences at Lake Maxinkuckee, in 

 northern Indiana, three or four of us, within a few hours captured about 

 thirty specimens of 3/. geograpJdca. These specimens were almost invaria- 

 bly taken in the water near the shores of the lake where the bottom was 

 covered with the shells, living and dead, of Virljiara coiitrctoidcs. Seven of 

 the terrapins were taken home and kept some days in a washtub partially 

 filled with water. When they were taken out, there were found on the 

 bottom of the tub large numbers of the opercula of that water snail. In the 

 alimentary canal of one terrapin were found these opercula, as well as the 

 remains of crayfishes, and what appeared to be the cases of some species of 

 caddis- worm. The masticatory surfaces of the older specimens were found 

 to be much worn. The crushing surfaces of Dr. Baur's recently described 

 M. ocuUfcra are rather narrow, while the cutting edges of the jaw are very 

 sharp. The indications are that the food does not consist of mollusks, but 

 rather of some soft vegetable and animal substances. 



Most, if not all, the species of this genus are extremely variable in the 

 size of the head. In the paper referred to above, Prof. Garman attempts to 

 give us the characters that distinguish gcograpJiica from pseudogeograpjhica^ 

 and among such difierential characters is the size of the head relative to 

 length of the carapace. (Uvgrapldca is stated to have a large head; pscx- 

 dogeograplika a much smaller head. He also presents measurements that 

 appear to prove his position. Dr. Holbrook long ago described a specimen 

 of geographic^ under the name of Emijs megaccpliala, the name being sug- 

 gested by the massive head. Some years ago Dr. Gray suggested that the 

 large head might be a sexual character, but he did not state which have the 

 big heads, the males or females. Through the kindness of Dr. Stejneger, 

 I have been permitted to examine all the specimens of both species that 



