Williston.] Turtles. 365 



Eight marginal bones are present, including the pygal. 

 Whether they are all from the same side or not I do not know ; 

 but all are different. Lying in position, with the anterior pro- 

 jection touching nearly the posterior end of the united carapace, 

 is the pygal which is figured, the surface which is represented 

 being the upper one, and the attached marginal belonging to 

 the right side. Lying beneath it, near the margin, were two 

 small caudals, one of which is shown in the plate. The pygal 

 and adjacent marginal are very flat bones, very thin on the 

 outer margin, somewhat roughened on the anterior part. A 

 fragment of the attached left marginal is present, but is not 

 shown in the figure. The sutural union, here as elsewhere, is 

 firm. 



Length of pygal 97 mm. 



Width at the ends 42 



Width across the middle 61 



Thickness near anterior border 6 



Length of adjacent marginal 64 



Width 45 



Thickness 5 



Lying in contact with a hyo- or hypoplastron is one complete 

 marginal, and portions of two others partly detached. The 

 bones here are r elongate and narrow, with interdigitated sutural 

 ends. On the lower side of the one exposed they are flat, with 

 the inner margin thin, but somewhat thickened on the outer 

 part. 



Length of lateral marginal 130 mm. 



Width at one end 35 



Width at other end 27 



Width of contiguous marginal 37 



Thickness near middle 6 



The half of two contiguous marginals lying over the left 

 scapula shows the outer part thicker, from nine to eleven mm. 

 in thickness; the inner part very thin, and, near the middle, 

 below the thin border a shallow horizontal pit, which may have 

 been for the reception of a rib. The greatest width of these 

 bones is thirty-nine mm. 

 18— iv 



