8 HEPATICAE AND ANTHOCEROTES OF CALIFORNIA 
dichotomus are represented on the Californian coast by the close 
analogues, Porella Roellii, Riccia trichocarpa апа Anthoceros phy- 
matodes, their nearest relatives in the eastern United States being 
much farther removed ; again, a species may be very common in 
Europe and very rare in California or, vice versa; and facts like 
these are wholly lost sight of in merely numerical comparisons of 
what we choose to regard as species. A few special considerations 
serve to emphasize the affinity of the California hepatic flora with 
that of Europe, particularly with that of the Mediterranean region. 
We have, to begin with, five species of the genus Asterc//a in Cal- 
ifornia and the same number in Italy. Inthe eastern United States 
there is but one representative of this genus. Ten species of Riccia 
—a genus which seems to find its best development in southern 
Europe and northern Africa—are known to occur in California. 
Of these, one cannot be distinguished from a species otherwise 
known only in southern France and Italy, and one or two others 
are closely allied to species peculiar to the same regions.  Zargi- 
onia hypophylla, too, is another link in the chain that binds Cali- 
fornia to the warmer parts of Europe. This genus is absent in the 
eastern states, but what seems to be the very same species is found 
sparingly in the British Isles and central Europe, is more common 
in northern Italy, andis said to become very abundant in the south- 
ern portion of the peninsula. One rather common Californian 
hepatic seems to be identical with Cephalozia Turneri—one of the 
rarest of the Old World species, occurring in limited quantity at 
a few localities in the British Isles, France, the Canaries, Corsica 
and Algeria. No stations for this plant intermediate between Cal- 
ifornia and the Old World are known, but it has been collected near. 
San Diego and there is a probability that this species, like Zargi- 
ота hypophylla, will be found to extend into Mexico. 7; argionia 
is represented in Mexico by two forms which were once considered 
distinct species but which have recently been reduced by Herr 
Stephani* to 7. hypophylla. The presence of this peculiar genus 
Targionia in Mexico, the Canary Islands and Africa, and its absence, 
so far asis known, in eastern Asia suggest the possibility of some pre- 
historic land communication across what is now the Atlantic Ocean. 
The possibility of spores or entire plants finding their way across 
* Bull. Herb. Boiss. 6:764. 1898. SPP 
