440 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



look a little forward; tliey are situated higli m the head. The jaws are 

 irregularly but quite finely serrated, the margins being almost in a 

 straight line. The sheath of the upper jaw is very high, between the 

 snout and the eye, but becomes narrovred abruptly under the eye. The 

 neck is of moderate length, with granulated skin. 



The anterior extremities are large, stout, and more or less compressed 

 in the anteroposterior direction. The claws, five in number, are 

 short, stout, and not curved. The scales on the anterior aspect of the 

 arm are all api)roximately equal in size. Those on the exterior edge 

 are a little larger. On the posterior surface the scales decrease in size 

 gradually from the exterior to the interior edge. 



The posterior extremities are terete, the feet elephantoid, the soles 

 being large and round in contour. The scales surrounding the edge of 

 the sole are large, the two posterior ones being very thick and broad. 

 The four nails or claws resemble those of the fore feet, but show a 

 slight tendency to curve. There are two or three prominent scales on 

 the posterior part of the thigh. 



The tail, although very short, is considerably longer than tliat of X. 

 pohjphemiis. 



The general color of the whole animal is brown. The centers of the 

 plates of the carapace in the young, and in some adult specimens, is light 

 tawny yellow. The color of the plastron is usually a little lighter than 

 the general color of the carapace. 



In this descrijition I have follow^ed as closely as possible that given 

 by Dr. Holbrook, for X. poIypJiemiis, in order that the two may be con- 

 trasted. 



Specific distinctions. — The leading difference in structure between 

 X. polypJiemiis and X. Agassisii, one which is constant in all ages, is in 

 the size of the fore feet as compared with the size of the hind feet. 

 This distinction may be formulated as follows: The distance from the 

 base of the first claw of the hind foot to the base of the fourth claw 

 equals the distance from the base of the first claw of the fore foot to 

 the base of the third claw in X. polyphemus ; the fourth claw in X. 

 Agassizii. 



Again X. polypliemus^ at all ages, has the anterior end of the plastron 

 bent upward quite shari)ly toward the carapace, a character which does 

 not occur in X. AgasaizH. The inguinal plates of the former species do 

 not usually exceed four in number — one large one and two or tbrce small 

 ones internal to it — and are set obliquely. Those of X. Agassizii are usu- 

 ally five or six in number — two large ones and three or four small ones 

 between them — and are set vertically. X. polyphemus has one scale on 

 the inner aspect of the knee-joint of the fore leg very much larger thiin 

 the others covering that member, while in Agassiz's Tortoise all are 

 approximately equal. This character is most noticeable in the young. 

 The horny sheath of the upper jaw extends further back of the eye in 

 X. polyphcmus than in X. Agassizii. Other characters of less importance 



