26 TESTUDO POLYPHEMUS. 



Description. The shell is remarkably depressed, nearly flat above, with its 

 margin entire, slightly revolute in front, and incurvated posteriorly. The vertebral 

 plates are five in number; the anterior is pentagonal, presenting an obtuse angle 

 forward; the remaining four are hexagonal, the posterior irregularly so. The 

 first lateral plate is irregularly triangular, with its basis rounded and joined to 

 four marginal plates; the second and third are pentagonal, with an acute angle 

 above, passing in between the vertebral plates; the posterior is irregularly 

 quadrilateral, the longest border directed downwards. The marginal plates are 

 twenty-four in number; the intermediate or nuchal is irregularly quadrilateral, 

 and largest behind, where it joins the first vertebral; the supra-caudal plate is 

 single, very large, having twice the extent in the horizontal that it has in the 

 vertical direction, its lower border is incurvated, which gives this plate a remark- 

 able bulging appearance. The first marginal plate is pentagonal, the second 

 square, the third irregularly quadrilateral, and the fourth pentagonal; the four 

 succeeding plates are quadrilateral, and of greater elevation than breadth, 

 slanting a little backwards; the ninth, tenth, and eleventh are irregularly 

 quadrilateral; the tenth having its posterior and superior angle truncated, where 

 it joins the posterior vertebral plate. All these plates are marked with concentric 

 strioB, which are most remarkable on the lateral and marginal, and are often 

 wanting on the vertebral plates. In many old individuals these disappear 

 entirely, and leave the shell perfectly smooth. 



The sternum is thick and firm, prolonged beyond the shell in front, and deeply 

 emarginate behind. The gular plates are quadrilateral, and unite to form a 

 spade-like process, with its anterior extremity generally entire, but occasionally 

 emarginate; the brachial plates are quadrilateral, with their outer and anterior 

 angles rounded, the anterior border shortest and oblique in direction to receive 

 the gular plates; the thoracic are very irregularly pentagonal, narrow, and of 

 great extent in the transverse direction; the abdominal are quadrilateral and very 

 large; the femoral are also irregularly quadrilateral, with the longest border 

 directed forwards; the subcaudal plates represent oblong squares, and are most 



