18 TRIONYXMUTICUS. 



fore-arm; the fingers are five in number, fully palmate, the three anterior alone 

 provided with nails. The posterior extremities are short, flat, especially at the 

 tarsus, which sustains five toes, fully palmate, the web even reaching along the 

 posterior margin of the leg; the three anterior toes only are provided with nails; 

 the two posterior extend the web; behind the little toe is seen a large scale. 

 The tail is still shorter than in the Trionyx ferox; it seldom passes beyond the 

 disk, and has the anus at the tip. 



Colour. The whole superior surface of the head, neck and extremities of the 

 animal is light umber coloured, marked here and there with numerous minute 

 and irregular dark spots. 



The sternum is white, with reddish lines, caused by the blood-vessels, with a 

 slight bluish tinge on the bony portion. The inferior surface of the extremities 

 is also white, but with a tinge of blue. The membrane of the feet or web is 

 bordered with yellow. 



Dimensions. Length of head. If inches; length of shell, 9 inches; breadth, 8 

 inches; elevation, 3 inches. 



Habits. The habits of this species are similar to those of the Trionyx ferox. 



Geographical Distribution. This animal has only yet been found in the 

 Mississippi or its tributary streams. 



General Remarks. The Trionyx muticus, which was first noticed by Lesueur, 

 though closely allied with the Trionyx ferox, is perfectly distinct, and is easily 

 recognised by the total absence of spines or tubercles on the cartilaginous portion 

 of the shell. Leconte, however, says he "cannot as yet consider it perfectly 

 distinct," and his observation led several European naturalists to adopt the same 

 opinion. Though the distinctive marks applied to this species by Lesueur are 



