246 



University of California. 



[Vol. 3. 



The plates of the plastron (Fig. 2) are less easily distin- 

 guished than those of the dorsal shield. The anterior border of 

 the epiplastron has been broken. The entoplastron is entire. 

 In shape it is almost quadrilateral. The hyoplastron is entire, 

 but its lateral boundaries are not clear. The hypoplastron is 

 incomplete posteriorly. Sutural contact between carapace and 

 plastron begins with the third marginal plate. 



The boundaries of the epidermal shields cannot be completely 

 followed on either carapace or plastron. On the carapace, 

 alternate costals are marked by the traces of the margins of the 

 lateral shields. The dorsal shields appear to have been long in 

 proportion to their width. In outline, they were hexagonal. 

 The first, second, and third dorsal shields maybe traced more or 

 less completely. The first dorsal shield completely overlapped 

 the second neural and the adjacent halves of the first and third 

 neurals. The second appears to have had an ec|ual extent, and 

 to have involved in a similar manner the fourth neural, and parts 

 of Uie third and fifth. Each marginal bears the traces of an 

 epidermal shield. So far as the traces of the shields can be 

 followed on the plastron, they agree with the usual arrangement 

 of these elements in Mylniiy.s. The anterior border of the 

 pectoral shield terminates at the base of the axillary notch. 



Measurements. 



Second neural, anteroposterior diameter (approximate) .... 50 mm. 

 Second neural, transverse diameter 55 



Third neural, anteroposterior diameter 50 



Third neural, transverse diameter 51 



Third costal, length (approximate) 182 4- 



Third costal, width at dorsal extremity 68 



Third costal, width at marginal extremity 42 



Fourth costal, length 181 



Fourth costal, width at dorsal extremity 55 



Fourth costal, width at marginal extremity 07 



Fifth costal, length ! 168 



Fifth costal, width at dorsal extremity 52 



Fifth costal, width at marginal extremity 37 



Sixth costal, length (approximate) 138 



Sixth costal, width at dorsal extremity (approximate) 38 



Sixth costal, width at marginal extremity (approximate).. 51 



