724 



EEPTILIA. 



behind, but in others it is of equal width at both ends. In the former case, the first 

 costal margin is convex and the second sinuous or concave. The posterior margin 

 is usually notched. The third shield resembles the second, but is usually a little 

 shorter and broader. Both these shields, however, are subject to elongation. The 

 fourth is almost invariably considerably broader than long, with the same costal 

 margins as in the third, with its posterior margin equalling the tliird costal margin. 

 The fifth is contracted near its anterior extremity, and the breadth of its anterior 

 margin almost equals one-half of its length. It is generally in contact with a 

 caudal and marginal, but sometimes with two of the latter. 



The sternum of the female is quite flat, but that of the male is very slightly 

 concave. The inguinal exceeds the sternal breadth in both sexes. In the young, 

 there is a slight lateral ridge, formed chiefly by the areolse disappearing with age. 

 The gulars are abruptly terminated, their anterior breadth nearly equalling the 

 united length of the gulars and postgulars, these plates being of almost equal length, 

 the gulars sometimes being the longest. The pectorals and abdominals are of equal 

 length, their sutures having a backward direction, which is most marked in adults, 

 especially in the abdominals. The pre-anals and anals are of equal length, the 

 pre-ano-abdominal suture being concave from before backwards and the pre-ano-anal 

 convex from behind forwards. The anal notch is widely triangular in adults, and 

 deeply arched in young specimens. 



Measurements of shells. 



The snout is moderately long, triangular above, and rather pointed, the breadth 

 between the anterior angles of the eyes exceeding its length. The breadth at the 

 angle of the jaws, below the tympanum, equals the distance from the tip of the 

 snout to the posterior margin of the tympanum. The breadth between the posterior 

 angles of the eyes is a little in excess of the distance from the tip of the snout to 

 the posterior canthas of the eye, measured along the side of the face. The height of 

 the muzzle, measured from the bottom of the premaxillary notch to its upper border, 

 equals the interval between its tip and the anterior angle of the eye. The maxiUary 

 plate is acutely notched in front with a well-marked denticulation on either side of 

 it ; the maxiUary margin is curved and not serrated. Tlie sides of the face are nearly 

 vertical, and the eye is moderately large and about the size of the tympanum. The 

 upper surface of the head is covered with a smooth skin, but there are a few small 

 plates behind the eye and above the tympanum, and a granular area between the 



