366 University of Kansas Geological Survey. 



Plastron. 



All the plastron was originally preserved, but part has been 

 lost, and some has been necessarily injured or destroyed in get- 

 ting at the bones lying between it and the carapace in the hard 

 matrix. Lying contiguous with the upper end of the right 

 humerus is a large, thin, flat bone which is evidently the epi- 

 plastron. The bone had sustained injuries or decomposition 

 before fossilization, or was of a partly cartilaginous nature. 

 Its thicker, rounded border in gently concave and measures a 

 little over 200 mm. in length. Lying upon it and impressed as 

 though partly pressed into its substance, is evidently another 

 bone, which agrees better with the epiplastron of Chelone. It 

 is gently convex on the outer, concave on the inner border, ta- 

 pering to a point from the flat blade, and with well-marked 

 longitudinal grooves upon it. It measures 180 mm. in length 

 and has a width on the outer part of nearly thirty mm. If this 

 is the real epiplastron, I do not know what the broad bone is. 



A number of fragments of the hyo- or hypoplastron are pres- 

 ent, but, unfortunately, the portion figured cannot be united to 

 the remainder, through the loss of intermediate portions. That 

 they all belong to one bone, seems evident from the marked pe- 

 culiarities in the surface, color, and markings. The anterior (?) 

 denticulate margin has a width of ninety mm. ; the posterior 

 hypoplastral border (?) is incomplete, was not more than sixty 

 mm. in width and could not have had a close union with the 

 hypoplastron, if it touched it at all, as the extreme length in 

 this direction is only about 200 mm. The bone is thicker and 

 of firmer texture than is the carapace. The posterior end of 

 the xiphiplastron lies under the sacrum. It is only thirty mm. 

 in width, is thin and has four elongated denticulations. The 

 whole structure of the plastron appears to have been something 

 like that in Protosphargis veronensis. Whether the other ele- 

 ments of the plastron were present or not, I cannot now say. 



