What is the Olenellus Fauna. ^ — Matthew. 405 
stands alone, there being no otlier trilobite recorded as oc- 
curring with it. But the third form {(). hrogyeri) is grouped 
with a rich company of trilobite genera. 
The same condition in a less degree marks the third branch 
of the olenelloid stock [Hohnia kjerulji) which starts out in 
Norway and Sweden with only a few trilobite genera, all of 
ancient type, but becomes associated with more abundant and 
modern forms in America, i. e. tlie faunas with O. asaiihoidea 
and 0. vermontana. 
The following table is intended to express the supposed re- 
lations of the various branches of the olenellid stem to Para- 
doxides, as outlined in the preceding article. It is assumed 
that O. thompsoni and M. vermontana mark a separate sub- 
favina from E. asaphoides; if they should prove to be of the 
ssame sub-fauna as the latter, this should be placed higher up 
in the table. The transverse 4ine of the table is the base of 
the Paradoxides beds. 
To sum up the results of this review it may be said that the 
fauna of the Olenellus zone as set forth by Mr. Walcott, con- 
tains four elements: 
1st — A fauna that is pre-paradoxidean but contains no Olenel- 
lus [sensu stn'cto). — Newfoundland. 
2d — A fauna of the age of the Paradoxides beds — that of 
eastern New York. 
3d — A fauna whose place is uncertain, but probably at the 
summit of the Paradoxides beds, — that of western Vermont. 
and the St. Lawrence valley. 
4th — A fauna nearly cotemporary with the last, but perhaps 
later — that of several districts in the western part of North 
America. 
The above article records some facts, some inferences and 
some conjectures; if the last gain support from the first, the 
whole favors tiie view expressed by the author some years 
ago, in this journal, that the Cambrian system (at least so far 
as the Atlantic basin is concerned) is naturally divided into 
two parts (not three) so far as the faunas are concerned;* the 
lower marked by the "giant Oleni," the upper by the depau- 
perated forms of this family. This was the verdict of Salter 
*How is the Cambrian divided? A plea for the classification of Salter 
and Hicks. 
