1896.] Geology and Paleontology. 937 
species Z. apicalis has the apex of the spines dilated and sculptured on the 
superior or external surface, indicating the presence of a row of osseous 
shields covered by epidermis only, extending along the middle dorsal 
line. In the Trias, two such types have been previously known ; viz., 
the genus Typothorax Cope, from New Mexico, and Aétosaurus Fraas 
from Wiirtemberg. 
The discovery of the Permian form in question is important from 
various points of view. The discovery confirms again a hypothesis pro- 
posed by me, several years previously (NATURALIST, 1885, p. 247, 
Transac. Amer. Philos. Soc., 1892, p. 24). It presents us with what 
had been previously wanting, forms ancestral not only to the Triassic 
Reptilia above referred to, but also ancestral to the order of the Testu- 
dinata, which according to Quenstadt and Baur appears first in the Trias. 
The discovery also brings to light an interesting case of homoplassy, 
since we have two families in no way allied to each other, the one a 
Batrachian, and the other a reptile, presenting an identical character, 
and which is so closely similar in the two, that the carapaces cannot 
be well distinguished on an external view. Internally, however, the 
characters differ widely. In the case of the Reptilian family (Otoceel- 
ide) the structure is what one finds in the Testudinata and Pseudosu- 
chia (Typothorax); while in the Batrachian it is constructed by an 
expansion of characters already known in other Stegocephalia. 
For the accompanying illustrations I am indebted to the American 
Philosophical Society. 
PLaTe XXI. 
Otocelus testudineus Cope, From above x.66. 
PLATE XXII. 
Dissorhophus articulatus Cope, x.82; 1 above; 2 below; 3 anterior 
view.—E. D. Cope. 
Ameghino on the Evolution of Mammalian Teeth.'—The 
discoveries of M. Ameghino in Argentina have put him in a position to 
throw a great deal of light on the evolution of the Mammalia. Several 
problems which are presented by general Mammalian dentition should 
be greatly elucidated by his material, and some of those suggested by 
the Toxodont and Edentate types are within his reach almost to the 
exclusion of other investigators. He has already made important con- 
1 See Evolution des Dents des Mammiferes par Florentino Ameghino. From 
the Bull. Acad. de Ciencias de Cordoba, XIV, p. 381; Buenos Ayres, 1896. 
65 
