11 



The typical specimen equals those of the large land tortoises 

 of the Eocene in dimensions.' 

 Discovered by C. H. Sternberg. 



Polythorax missuriensis, Gen. et sp. nov. 



Char. Gen. — Plastron with contracted fixed lobes and wide 

 bridge; carapace with well-developed marginal bones; mandibular 

 ramus narrow; alveolar face with acute external margin; the 

 symplvysis neither produced nor recurred. Dermal scuta every- 

 where distinct, those of the plastron the usual ones, with the addi- 

 tion of the two marginal intergulars, and two large interhumerals. 

 The latter scuta are separated from the numerals by sutures run- 

 ning parallel with the humeral margin of the anterior lobe between 

 the gular and pectoral scuta. 



In the possession of interhumeral scuta, Polythorax differs from 

 any known genus of Testudinata. The general structure is much 

 like that of Adocus and Baena, with nearer resemblance to the 

 latter in its double intergular scuta. It is impossible to ascertain 

 whether there are intersternal bones, as the plastron is coossified 

 throughout. The presence or absence of interna arginal scuta can- 

 not yet be determined, although it is clear, that if existing, their 

 position is quite external. 



This genus is interesting as connecting in its stratigraphical 

 position allied types of Cretaceous No. 5 (Adocus), with those of 

 the Wahsatch and Bridger Eocenes (Baena). 



Char. Specif. — Carapace with openly dentate posterior border. 

 The surface is irregularly swollen, especially on the median line 

 near the margins of the vertebral scuta. The vertebral scuta are 

 wide, the costals short, and the marginals narrow. The anterior 

 lobe of the plastron is a little shorter and more contracted than 

 the posterior; its base is narrower than the antero-posterior extent 

 of the bridge. Its extremity is rounded, while that of the pos- 

 terior lobe is truncate with rounded angles. The gular and in- 

 tergular scuta are each wider than long, while the interhumerals 

 are much longer than wide. The humerals are narrow while the 

 pectorals are wide from the anterior position of the pectoro- 

 humeral suture. Each anal scutum is longer than wide. 



The surface of the plastron is obsoletely but coarsely rugose ; 

 the roughness greatest anteriorly, where it consists of short raised 

 lines irregularly disposed. 



