104 



more convex longitudinally, from the thickening of the bone. The margins 

 are irregular, from the projection of many digitations. Some of these are 

 broad and flat; others are narrow. They are frequently two deep, and the 

 fissures separating them occasionally extend far toward the middle of the 

 bone. The convexity assumes the form of a low ridge toward one end of 

 the bone. At the point where this reaches the margin, the latter is in all the 

 four plates, thickened, and composed of several layers of packed osseous radii. 

 When found, the ribs laid across these shields, one of them occupying the 

 position of a radius to one of them. These shields are much larger than the 

 marginal bones. 



Measurements. 



M. 



Length of " No. 10 "(21 inches) ■- 0.535 



Width of " No. 10" (broken) 0.400 



Thickness at the middle 0.014 



Length of " No. 9 " 0.530 



Width of "No. 9" (much broken) 0.350 



Thickness at the middle 0.013 



The lengths and breadths given are a little below the truth, owing to 

 the loss of the exceedingly thin margins. 



Turning to the endo-skeleton, the vertebrae deserve mention. There are 

 more or less complete examples of five of these; in two, both centrum and 

 neural arch, in two neural arch, and in one centrum, are preserved. These 

 have been recognized chiefly by their neural arches, which are separate. 

 They are in form something like an X, the extremities of the limbs carrying 

 the zygapophysial surfaces. The only point of contact with the centrum is a 

 wide process, which stands beneath the anterior zygapophysis, and spreads 

 out footlike obliquely forward and outward, to beyond the line of its anterior 

 margin. Its surface extends nowhere posterior to the surface of the zygapo- 

 physis above it, but a little farther inward. Its outer margin rises ridgelike 

 to the under side of the neural arch, and each one, forming a semicircle, forms 

 the boundary of the neural canal, and, turning outward, forms the inner 

 boundary of the posterior or down-looking zygapophyses. The space between 

 these apophyses is roofed over, so as to produce a shallow zygantrum, which, 

 however, only seems to roof over the deep emargi nation of the neural arch 

 of the vertebra immediately following. The anterior zygapophyses are often 

 broken away, so that the neurapophysinl supports look like the missing pair, 

 when the difficulty ensues that both pairs look downward. The lop of the 



