Reptiles and Amphihians of Illinois. 237 



Carapace of small example 3.50 long, 2.87 wide, and 1.37 

 high with plastron. 



Throughout Illinois in the larger streams and lakes; abund- 

 ant. Nippersink Lake, Green River in Henry county, Ogle 

 county, Quincy, Peoria, Pekin, Little Wabash River, St. Fran- 

 cisville, Little Fox River at Phillipstown, Cairo. 



This is a characteristic species of our waters and occurs in 

 countless numbers in lakes, rivers, and flood-ground pools. 

 Half the individuals which one may see perched upon logs dur- 

 ing a day's boating in August would, if examined, prove to 

 be of this species. It is exceedingly common in the Illinois 

 and Mississippi rivers, where it is known ( with M. lesueuri, 

 from which it is not discriminated) as the mud turtle. It is 

 timid and inoffensive in disposition, always sliding from bank 

 or log when approached, and even when made captive shows 

 none of the ferocity of " leather backs " and snapping turtles. 

 The great strength of its jaws (unsurpassed in massiveness 

 among our Chelonia) would enable it to inflict serious wounds 

 if it were so disposed, and it is a little surprising to find such 

 efiicient weapons of offense unaccompanied by special rugged- 

 ness of temper. The unusual width of the masticatory sur- 

 faces of the jaws suggests Mollusca at once as the proper food 

 of this turtle, and an examination of the contents of stomachs 

 from numerous examples, young and adult, shows that it de- 

 pends entirely on these for sustenance. Small examples taken 

 at Quincy, Illinois, had eaten nothing but the gastropod VaU 

 vata tricarinata. 



Family OINOSTERNID^. 



Shell bony, covered with horny plates. Carapace convex, 

 with five dorsal, eight costal, one nuchal, twenty marginal, and 

 two caudal plates. Plastron small or moderately large, rounded 

 before, truncate or emarginate behind, consisting of three por- 

 tions, the median of which is covered only by the abdominal 

 plates and is immovably united to the carapace, while the ante- 

 rior and posterior lobes are attached to the median fixed portion 

 by transverse hinges. A single gular plate. Pectorals not 

 forming part of the bridge. Axillary and inguinal of each 



