103 



A very long, gently-curved bone is probably the marginal extending on 

 one side of the nuchal. It is nearly twice as long as the others, and has an 

 extensive and thin superior lamina. Its ? anterior part is in one plane; but 

 the margin soon thickens, and displays a rather wide infero-external face. It 

 appears to have had an inferior lamina on its posterior half, which made an 

 angle with the face just described. An oval cavity included looks as though 

 designed for the apex of a rib. 



The variation in the lengths of these marginal bones is noteworthy. I 

 give measurements, premising that a few lines may be added to the extremi- 

 ties of some for lost digitations. 



Measurements. 



M. 



Length of the long anterior (11 inches) 0. 28 



Width of the long anterior (some lost) 0. 135 



Length of the lateral with the inferior face .., 0. 195 



Width of the lateral (much lost) 0.110 



Length of the lateral with narrower inferior face 0. 206 



Width of the lateral (much lost) 0.115 



Length of one with the interior lamina 0. 14 



Width of one (some lost) 0.086 



Length of a thinner, no inferior plate 0. 193 



Lengtli of a still thinner, no inferior plate 0. 182 



Width of a still thinner (broken) 0.137 



Length of the thinnest _ 0. 162 



Width of the thinnest (nearly complete) 0. 160 



? Caudal length 0.117 



? Caudal width 0.150 



The shortness of the marginal with large interior lamina is noticeable, as 

 also the same peculiarity in the caudal. As compared with marine turtles, 

 difference is to be observed in every particular. Such are the lack of sutural 

 union; the laminar character; the great extent of the superior and distinctness 

 of lower laminae. There is no trace of epidermal sutures visible anywhere. 



A single symmetrical plate appears to have belonged to the middle line 

 of the back or nape. It was subtriangular in outline, all the margins very 

 thin, and with an obtuse keel extending on the middle line, on the posterior 

 (or anterior) two-thirds to the apex. This ridge disappears in ?front by a 

 gradual expansion The surface is marked by lines of minute pits and 

 grooves, which radiate from the base at the (?) front of the ridge. Length, 

 CT.135; width, m .21. 



The lateral dermal bones preserved, are two entire, and large parts of 

 one or two others. They have an irregular oval outline, and are slightly 

 dished on the inferior surface or that next the ribs. The upper surface is 



