756 REPTILIA. 



There are specimens, however, in which the proportion is reversed, and there are 

 examples with first vertebrals with straight lateral margins divergent from behind 

 forwards, and in these cases the shield is nsually as long as broad : the posterior 

 margin is sinuous. The longitudinal axis of the plate is occupied by a distinct 

 ridge. The second, third and fourth vertebrals are nearly quadrangular and 

 almost of equal breadth, the first-mentioned being the narrowest. Their lateral 

 margins are all more or less parallel but sinuous, and the posterior margins 

 concave from behind forwards. The fifth forms a broad suture with the fourth, 

 and its lateral margins are slightly contracted in their anterior fourths, and the 

 length of this shield varies considerably. One marginal is in contact with the 

 first vertebral, four with the first costal, and three touch the second, tbird and 

 foiu'th ; the fifth vertebral only being very narrowly in contact with the tenth 

 marginal. The caudals, in some specimens, project backwards slightly, as if com- 

 pressed, but the caudal notch is absent. 



The gulars project beyond the post-gulars, but are truncated in front, and their 

 suture exceeds that of the post-gulars. The poster o-post-gular suture is nearly trans- 

 verse in some, but in others forms a posteriorly obtuse angle. The pectorals 

 are a little longer than the abdominals, and the postero-abdominal suture is directed 

 backwards. The abdominals are the next longest shields equalling the post-gular 

 and half of the gulars, and standing in the same proportion to the preanals and anals. 

 The preanals are very little longer than the pectorals, and the anals equal the 

 pectorals and nearly one-half of the gulars. The anal notch is broad. The axillary 

 breadth equals one-half of the length of the sternum, and exceeds the breadth 

 of the sternum at the groin. 



In younger females, the shell is more rounded, and in very young specimens 

 about 3*25 inches long, the shell is nearly round, and the first and second marginals 

 slightly reverted, the vertebral ridge being well developed, almost as in Pangshura, 

 forming a prominent truncated spine on the third vertebral and all but absent 

 on the fifth shield. The sternal ridge is strongly marked. The gulars nearly 

 equal the post-gulars in length ; the pectorals, the abdominals, and the preanals 

 equal nearly the anals ; the two last pairs of shields being only a little longer 

 than the first. 



On carefully examining about 100 living examples of this species, I found that 

 there were two distinct forms of shell, one a large, full and globose shell, and the other 

 a more depressed and more elongated oval ; the animals of the former characterized 

 by short tails, and those of the latter with long tails, but that with these exceptions 

 the animals of* the two forms of shell were identical. On dissecting a number of 

 examples of each type, it was found that the deep and shortly oval shells with the 

 short-tailed animals were females, and the longer ovals and more depressed shells 

 with long-tailed animals were males. 



The adult male is a narrower and more elongated oval than the female and 

 considerably smaUer, measuring 6 inches in a straight Hue. It difPers also in 

 form by the less arched character of the shell, both antero-posteriorly and trans- 



