No. I.] RELATIONSHIPS OF PROTOSTEGA. 39 
In a recent paper (43), Dr. O. P. Hay has described portions 
of the plastron of a large specimen of Protostega, and attempted 
a restoration. The materials on which his restoration was 
based were the almost complete hyo- and hypo-plastra of one 
side and a fragmentary nuchal. Regarding the plastron he 
says (p. 58): “In Zhalassochelys the anterior end of the epi- 
plastra extends in front of a line joining the bottoms of the 
excavations for the fore limbs a distance equal to that from the 
bottom of the excavations for the fore limbs to those of the hind 
limbs. This, in the Pvotostega plastron before me, amounts to 
84 cm. The xiphiplastra of Zhalassochelys extends behind 
the excavations for the hinder limbs as far as do the epiplastra 
from the anterior excavations. If these proportions hold good 
for Protostega, the whole length of the plastron would amount 
to at least 2.4 meters’’; and further (p. 59): ‘had the breadth 
of the body of Pvotostega possessed the same ratio to the 
length that we find in Thalassochelys, the lower side of the 
animal would have been about 2.2 meters wide.”’ In regard to 
the fontanelle: “if we have placed the plastral bones aright, 
there is left between them a great fontanelle. Where the 
hypoplastra are widest, this is about 43 cm. in width, and oppo- 
site the union of the hyo- and hypo-plastron about 90cm. This 
is somewhat smaller, however, than the fontanelle found in 
Protosphargis, and much smaller than that of Dermochelys.” 
The head he estimates as 32 cm., from the snout to the end of 
the occipital condyle, and concludes as follows (p. 62): “The 
length of the carapace of Chelonia has a ratio to the plastron 
of about 31 to 24. Hence the length of the carapace of my 
specimen must have been close to 3.1 meters. The neck of 
our living marine turtles projects beyond the front of the cara- 
pace a distance equal to at least 4 of the length of the carapace. 
Hence we are safe in allowing 50 cm. for the neck outside of 
the shell. We have, therefore, for the length of this turtle the 
following figures: 
ead Mgnt ih ice Noni shee UILeLeTS 
Neck beyond carapace . . .50 “ 
Carapacev pment! tiie couse LON pace 
POtali Msc shi hol ia wise cnashy os Meee SOB eee) 
