270 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
WIERLAND GROUP. 
This series, held together by the presence throughout of Echino- 
sphaerites aurantium, shows a decided change of faunas from bottom to 
top. The fauna of the oldest formation, the Dubowiki, is dominated 
by its asaphids, but these trilobites immediately lose their importance, 
and though they continue through the remainder of the Ordovician, 
they are present in limited variety and numbers. As previously 
stated, there are thirteen species which pass over from the Walchow 
and Kunda into the Dubowiki, but very few of them survive beyond 
this formation. 
The Wierland fauna is, however, in general, an outgrowth of that 
which preceded it in the same area. Among the trilobites, notable 
new arrivals in this group are: — Chasmops, Sphaerocoryphe, Pseudo- 
sphaerexochus, Sphaerexochus, Acidaspis, Hoplolichas, Homolichas, 
Cyphaspis, Lonchodomas, and Ogygites (Basilicus of Schmidt). All 
of these genera, with the exception of Acidaspis and Cyphaspis could 
have arisen as modifications of types already in this region, so that we 
have, as true invaders only these two genera. 
Among the brachiopods the important new genera are Christiania 
and Oxoplecia. The place of origin of these genera is unknown, but 
from their short ranges and limited variety in Russia, it seems probable 
that they are present there as migrants. Other brachipods intro- 
duced here are Plectambonites and Rafinesquina, but the dominant 
forms are the Clitambonites and Porambonites which continue from 
the formations below. 
Among the gastropods, Bucania, Cymbularia, Eccyliopterus, 
Salpingostoma, and Subulites make their appearance first in this 
formation; while of the echinoderms, we find here the oldest species 
of Caryocystites, Echinosphaerites, Cryptocrinites, Cystoblastus, 
Cyathocystis, Hemicosmites, Hybocrinus, and Protocrinites. Among 
the sponges, Receptaculites is introduced at this time. 
In running over this list of genera newly introduced into the Russian 
Ordovician during Wierland time, we are struck by the fact that we 
are here dealing with more familiar genera. Barring some of the 
cystids and one or two other genera, all these genera are known in 
America, and most of them from the Middle Ordovician. The greater 
part of these genera seem to have developed in the North European 
basin and to have migrated thence to America. 
Certain of the genera are, in America, restricted to a belt along the 
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