180 



Annals of the Carnegie Museim. 



The plastron (Plate IX) has the hinder extremity missing. The 

 total length cannot, therefore, be accurately determined ; but it must 

 have been close to 205 mm. The breadth, measured on the meso- 

 plastra and following the curves, is 186 mm. The whole width of the 

 animal was, of course, somewhat greater. The median region is slightly 

 concave to a ridtre which runs from the free border of the front lobe 



Fk;. 2. Bacna callosa W^y. Diagram of plastron. yi,'*,y natural size. The names 

 of the bones are indicated on the left side of the figure ; of the scutes, on the right 

 side. !■/.//., epiplastron ; c;//.//. , entoplastron ; //rc/A , hyoplastron ; w^.f.//., meso- 

 plastron ; Jiyp.pL, hypoplastron ; xi.pl. , xiphiplastron ; /.^/<., intergular ; gu., gular ; 

 /mm., humeral; pect., pectoral; ab.d. abdominal ; y^'w. , femoral; aft., anal. 



to that of the hinder lobe. I'rom this ridge the lower surface slopes 

 upward and outward to the borders of the plastral bones. The 

 bridge has a fore and aft extent of 87 mm. The anterior lobe is short 

 and narrow. The length is 52 mm.; the width at the base, 72 mm.; 

 at the hinder ends of the epiplastra, 38 mm. The latter bones are 

 small and they meet along the midline, in front of the entoplastron, 



