PHYLOGENY OF SHELL OF TESTUDINATA 429 



Turning, now, our attention to the peripheral bones, we find, 

 at the peaks of the tooth-Hke processes along the border, areas 

 so similar to those found on the neurals and costals that we can 

 hardly doubt that they were once covered each by a thin bone. 

 These may have been lost during preparation of the skeleton. On 

 the left fourth peripheral (fig. 4) there is a fragment of one of 

 these bones sutured to the peripheral. It is only 10 mm. long 

 and 4 mm. wide, but evidently it was once about 15 mm. long 

 and 5 mm. wide. A part of it appears to have been absorbed. 

 On the upper surface of the peripheral an impressed area ex- 

 tends 8 mm. from the edge, and the bone mentioned appears to 

 have once covered this area. The latter does not show well in 

 the figure; but on the lower face of the peripheral the impressed 

 surface is larger and deeper. On no other peripheral is there 

 found a separate bone, but the surfaces for receiving them are 

 usually distinct, sometimes conspicuously so. Figure 5 of the 

 plate presents a view of the border of the first and of a part of 

 the second right peripherals of carapace 7167. The view is 

 partly from below. The lines radiating from the letters, a, a, 

 call attention to the rough surfaces which appear to have sup- 

 ported bony plates. Similar surfaces are present even on the 

 projecting points of the pygal bone. These appear to have been 

 spread out as thin laminae over the upper surface as far forward 

 as the sulcus in front of the marginal scutes. 



Another carapace (no. 6596) appears to have belonged to an 

 old captive individual, and the borders of the shell are consid- 

 erably worn, especially over the hind legs. No bones corre- 

 sponding to the superficial ones above described are observable, 

 but their former presence is in some places distinctly indicated. 

 On the front of the nuchal scute area (fig. 6, a) there is, however, 

 a bone 16 mm. long from side to side and 3.5 mm. wide. This 

 is placed at the center of growth of the nuchal scute. The 

 third carapace (no. 5911), apparently belonging to a species 

 different from the others, appears to present no features that 

 add to or subtract from what has been observed in the others. 



Interesting results are secured in a study of the plastra. That 

 of the specimen no. 7167 must first receive attention, and a 



