NooT: | RELATIONSHIPS OF PROTOSTEGA. 51 
We may then conclude that Protostega is a connecting link 
between Dermochelys and the Chelonttdae. The evidence for 
this position of Dermochelys may be stated as follows: 
(1) The bones of the head are referable to those in the head 
of the Chelonitdae. The intermediate form is represented in 
Protostega. 
(2) The cervical vertebrae are alike in both families. The 
fourth is biconvex and the articular surfaces between the sixth 
and seventh are flat. 
(3) The plastron of Dermochelys is a reduced form of the 
plastron of the early Chelonitdae. The intermediate stages are 
represented in Protostega and Protosphargis. 
(4) The carapace is composed of dermal ossifications; they 
appeared after the bony carapace had disappeared by ossifica- 
tion of the integument. The original carapace was removed 
by the enlargement of its lateral fontanelles. An intermediate 
form, with the carapace gone and the separate ossifications not 
yet formed, is represented in Protostega and Protosphargis. 
(5) The process of the disappearance of the peripherals is 
known in all stages. 
(6) The nuchal plate of Dermochelys is provided with a proc- 
ess for articulation with the last cervical; this process is absent 
in Protostega and present in the Chelonizdae. The plan of 
development could not have included, in the time occupied, its 
loss and subsequent reacquisition. The line of Dermochelys 
rather took origin after the process was developed in the main 
stem of the Cheloniidae. 
In conclusion I wish to express my thanks to Dr. G. Baur 
and to Dr. S. W. Williston for material most kindly furnished 
me for these studies. 
PALEONTOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO, 
April, 1896. 
ADDITIONAL NOTE. 
Since the above was written Mr. G. R. Wieland has described 
the remains of a large sea turtle from the upper cretaceous of 
