44 CASE. [VoL. XIV. 
Lytoloma of the upper cretaceous and lower eocene has 
eleven peripherals; 1, 2, and 10 are free, the third has a 
small pit for a process from the plastron. According to 
Baur (22), the specimens in the Bruxelles Museum have no pit. 
The nares and orbits are directed upward. The palatal aspects 
of the temporal fossae are wider than long. The ecto-pterygoid 
process is near the anterior extremity of the pterygoid. The 
posterior nares are in the hinder half of the cranium. The 
vacuities of the shell are even less than in the recent 7halasso- 
chelys. The nuchal in the eocene form has the beginning of a 
process for the cervical. 
Argillochelys from the eocene has the orbits and nares 
directed slightly upward. The palatal apertures of the temporal 
fossae are as wide as long. The ecto-pterygoid process is at 
the antero-external angle. The posterior nares are in the 
anterior half of the cranium. The carapace was, probably, very 
close to that of Thalassochelys. 
Thalassochelys, eocene and recent, has more than 11 periph- 
erals, the addition taking place between the 1 and 3. I, 2, 
and g are free from ribs; there are no pits for the plastron. 
The carapace is completely ossified in the adult. The posterior 
nares are in the middle half of the skull, retreating as age 
advances. The nuchal has a process for the cervical ver- 
tebrae. 
Before attempting to interpret the facts just given, it may be 
of value to review briefly the discussion between Baur, Dollo, 
and Boulenger on the systematic position of Dermochelys, and 
the validity of the group Azhecae. 
Baur in 1886 (19) declared that the separation of Dermochelys 
from the rest of the Zestudines was a purely artificial one: 
«Diese Absonderung der Dermatochelyzdae ist keine natiirliche 
sondern eine absolut kiinstliche,” giving as his reasons: 
1. That the configuration of the skull and of its separate 
elements is directly comparable to that of the Chelonzidae, and 
especially to Eretmochelys. 
2. The cervical vertebrae are like those of the Chelonizdae, 
the fourth being biconvex. 
3. The nature of the claws. In Thalassochelys the first and 
