Prof. K. A. von Zittel—On the Mammaiia. 401 
The rocks in Wales classed as Dimetian, Arvonian, and Pebidian 
may or may not be equivalents of the rocks in Scotland called by 
the names Lewisian, Grampian, and Torridonian ; but at present it 
is far safer and certainly fairer that the groups should retain the 
names ‘given to them in the country where their positions were 
first recognized. 
IV.—Tue Groxrocgican DeventorpmMentT, Descent AND DistTRIBUTION 
oF THE Mammatia.! 
By Prof. Kart A. von Zitren, Ph.D., For. Memb. Geol. Soc. Lond. 
Professor of Palzeontology in the University of Munich. 
N a spirited treatise on the ‘Origin of our Animal World’ 
Prof. L. Riitimeyer,? in the year 1867, described the geological 
development and distribution of the mammalia, and the relationship 
of the different faunas of the past with each other and with that 
now existing. Although, since the appearance of that masterly 
sketch the paleontological material has been, at least, doubled 
through new discoveries in Europe and more especially in North 
and South America, this unexpected increase has in most instances 
only served as a confirmation of the views which Riitimeyer 
advanced on more limited experience. At present, Africa forms 
the only great gap in our knowledge of the fossil mammalia; all 
the remaining parts of the world can show materials more or less 
abundantly, from which the course followed by the mammalia in 
their geological development can be traced with approximate 
certainty. 
Mesozoic Hra. 
The oldest remains of mammals come from the Triassic rocks. 
Detached teeth of Microlesies and Triglyphus from the Rhetic beds 
of Wiirtemberg and England, a skull of Tritylodon and skeletal 
fragments of Theriodesmus from the Karroo beds of South Africa, 
prove the wide distribution of the unfortunately still very im- 
perfectly known Allotheria at the beginning of the Mesozoic period. 
If it is at present not yet possible to indicate the settled position 
of these small plant-eating or omnivorous animals in the zoological 
system, it yet remains certain that they can only be compared with 
the lowest organized of existing mammals, the Monotremata and 
Marsupialia; and neither in their dentition nor in the form of the 
skull do they show relations to Reptilia or Amphibia. Quite another 
group of primitive mammalia of small dimensions is indicated by 
two small lower jaws from the upper Trias of North Carolina. The 
genera Dromatherium and Microconodon remind one of Insectivora 
and Marsupialia, but they differ from both in the highly primitive 
1 Translated, with the permission of the author, by Dr. G. J. Hinde, V.P.G.S., etc., 
from the German, Aus den Sitzungsberichten der mathematisch - physikalischen 
Classe der k. bayer. Akad. d. Wiss. 18938. Bd. xxiii. Heft. II. pp. 137-198. 
The present treatise forms the concluding chapter of the 4th volume of the 
author’s Handbook of Paleontology, Munich, R. Oldenbourg, 1893. — 
2 Rutimeyer L. Ueber die Herkunft unserer Thierwelt. Hine zoogeographische 
Skizze. Basel. 1867. 
DECADE III.—VOL X.—NO. IX. 26 
