40 CASE, [VoL. XIV. 
The specimens just described afford material for quite accu- 
rate measurements, which give results different from those 
obtained by Cope and Hay, the main discrepancy being in 
the relative length of the carapace to its breadth. The present 
specimen shows the peculiar bent condition of the xiphiplastra, 
which was not indicated in the specimens described by the 
authors mentioned. This would account for a considerable 
reduction of the length of the plastron, and a still further 
reduction is quite certainly to be found in the condition of the 
epiplastra. In none of the known specimens has any trace of 
epiplastra been discovered, and neither in the specimen here 
described nor in Dr. Hay’s specimen can I find any trace of 
attachment of the epiplastra. Moreover, the anterior ends of 
the hyoplastra meet over the anterior end of the fontanelle. In 
the plate of Protosphargis given by Capellini the restored 
epiplastra extend beyond the exterior end of the hyoplastra a 
distance of one-tenth the length of the plastron as restored. 
This restoration is open to doubt, however, as the close resem- 
blance of Protosphargis to Protostega makes it possible that 
the distal ends of the xiphiplastra were incurved as in Proftostega. 
Only the proximal ends of both epiplastra and xiphiplastra are 
known. It may be assumed, however, for the purposes of this 
restoration, that the epiplastra extended in front of the hyo- 
plastra a distance of one-tenth the length of the plastron. 
The distance from the posterior edge of the conjoined 
xiphiplastra to the anterior extent of the hyoplastra is 1.15 
meters; adding to this one-tenth the length of the plastron, we 
have 1.27 meters, instead of 2.4 meters, as estimated by Hay. 
Fortunately, in the process of fossilization, the nuchal plate 
was pressed down upon the plates below, preserving them in 
their normal position, and rendering it possible to give exact 
measurements of the fontanelle. It was bridged in its anterior 
and posterior extent by the processes from the plastral plates, 
and at its widest part measured .§25 meters, instead of .go, as 
estimated by Hay. 
If we assume the ratio of the carapace to the plastron as 31 
to 24, as in Chelonia, the carapace was 1.64 meters long. In 
a three-fourths grown specimen of Chelonia the ratio of the 
