G. R. Wieland — Upper Cretaceous Turtles. 439 



an originally complete fossil shell, but the several parts secured, 

 although as numerous as in the preceding fossil, scarcely have 

 the fortunate situation making possible a similar restoration. 



The elements are all matrix-free, un crushed and disarticu- 

 lated, with the sutural faces all clearly outlined (save a small 

 outer border portion of the left side of the plastron). Also the 

 narrow to line-like hornshielcl sulci are all distinct in every 

 instance. Unfortunately, but a single example of the present 

 species is known with certainty. 



The plastral features of A. masculinus as shown in figure 

 8 are more nearly similar to those of A. tardus than to those 

 of any other known Agomphicl. Specific identity is however 

 clearly indicated by the slightly less robust form with rela- 

 tively larger hypoplastra and ventral hornshields, and an ento- 

 plastron of sub-rhombic instead of sub-isosceles outline. 



It is further to be observed that the doubly sigmoid antero- 

 posterior curvature of the plastron is greater than in any 

 other known species of Agomphus. Although this feature 

 does not clearly appear in the photographic figure 8, it is so 

 strongly accentuated in the fossil itself as to suggest that it is 

 an individual peculiarity denoting an old male turtle, or per- 

 haps better tortoise, whence the specific name. 



In addition a new specific character is exhibited by the com- 

 plete nuchal, and the third, eighth and tenth marginals accom- 

 panying the present plastron. These show that the marginal 

 hornshields anterior to the eleventh did not overlap the pleuro- 

 marginal sutures, and that the eleventh and twelfth did do so. 

 As this peculiarity is not present in either A. turgidus or A. 

 tardus, it in a sense unites Agomphus with Adocus since in 

 Adocus punctatus at least, a similar hornshield overlap begins 

 with the fifth marginal hornshielcl. 



(a) Measurements of the Plastron of Agomphus masculinus 



Type. 



Extreme length 17 cm 



Extreme width 13 



Length of bridge suture 10 



Distance between the axillar and femoral borders 7*9 



Length of the hyo-hypoplastral suture 5*5 



Length of inner hyoplastral suture . _ 4* 



Length of inner hypoplastral suture 3*5 



Length of inner xiphiplastral suture -4-5 



Lateral width of entoplastron 3*6 



Antero-posterior length entoplastron 3*4 



Greatest thickness entoplastron 1 -5 



Greatest thickness hyoplastron 1*8 



Greatest thickness hypoplastron 1*8 



Greatest thickness xiphiplastron 1*6 



