Geology and Paleontology. 451 
absence of projecting dentellated ridges upon the carapace ; by the 
margin of the dorsal armor not being rolled downwards; by the 
greater thickness of the carapace; by the apparent presence of 
horny plates; and by a skull proportionately shorter, wider, and 
with thicker bones. The cretaceous genera of the group Athece, 
viz., Protostega and Protosphargis, were without a dorsal armor. 
M. L. Dollo concludes that all the fossil Athece yet found in the 
an 
=“ a third genus near the former takes the name of Oxyodon- 
erium. 
M. Larrazet, as the result of his studies upon the character of 
the skin among fossil rays, divides them into three types: the 
first approximating to the modern Raja in form and size; the- 
second, which has placoid ossifications with a broad base and small 
Spine, forming the genus Dynatobatis; while the third, the dermal 
ossifications of which have a long spine and small base, forms the 
genus Acanthobatis. 
PLIOCENE AND PLEISTOCENE. — M. A. Villott thus classifies 
the alluvial deposits of Dauphinè: (1) Those of the high plateaus, 
some of which occur at a height of 700 metres above sea level, and 
which may be referred to tertiary times; (2) The pre-glacial 
deposits of the lower plateaus, forming the upper part of the high 
terraces, and entirely belonging to the quaternary epoch ; (3) The 
post-glacial alluvium of the lower terraces, formed after that great 
extension of the quaternary glaciers. The erosion of the valleys is 
cela principally to three different periods : (a) that which pre- 
th ed the quaternary epoch, and was the result of the bursting of 
© pliocene lakes — a necessary result of the last elevation of the 
