A C T I X E M Y S M A li M R A T A. 4^7 



sexes, and scarcely more prominent in the young than in the adult. 

 Differences are also observed in the depth of the body, some indivi- 

 duals, we believe to be female, being much deeper than others, which 

 we take as being the males. The same differences in the depth do 

 not hold good in the young, for amongst the latter we find the sub- 

 circular ones more depressed than those which have a subelliptical 

 shape. 



In the young, the periphery of the carapax is gently sloping on the 

 sides as well as anteriorly and posteriorly, whilst in the adult, it is 

 much steeper upon the middle of the sides, rather more plane ante- 

 riorly, very steep behind, and somewhat raised up on the sides of the 

 pelvic region. As to the very margin itself, it is nearly even, slight 

 indentations being observed at the junction of the scales. 



The scales on the back are; five vertebral ones, four on either side, 

 and twenty-five upon the periphery. The same number may be ob- 

 served in various genera and species : hence, neither generic nor specific 

 characters can be derived from it, although their form and proportions 

 may, to a certain extent, assist in the discrimination of the species. 

 The three middle vertebral scales are subhexagonal, broader than 

 long, considerably more so in the young than in the adult, as ex- 

 hibited by the accompanying figures. The anterior and posterior 

 scales of the same series are pentagonal, unequal, broader than long 

 in the young, whilst in the adult, the length increases at the expense 

 of the width. The lateral scales, constituting four pairs, are broader 

 anteriorly than posteriorly : the two middle pairs being much higher 

 compared to their width than the other two. 



The peripheral scales are twelve pairs, varying in size, and an odd, 

 rather exiguous one, situated upon the middle line, at the anterior 

 margin. The smallest pair are observed on the sides of the thoracic 

 region, and the largest on the sides of the pelvic region. 



The surface of the epidermis is, at first, wholly and minutely granu- 

 lar (figs. 13 & 14) ; degree by degree, as the growth proceeds, the granu- 

 lar surface recedes from the periphery of each scale, towards its centre; 

 the smooth zone, abandoned by the granules, exhibiting fine radiating 

 striae, and, when the growth is completed, the entire surface of the 

 epidermis is perfectly smooth. The bony surface underneath remains 

 more or less rugose and reticulated. 



The plastron is broad and subelliptical in its general outUne, and 

 overlapped by the carapax. When considered, however, in its detail, 



