APRIL 5, 1912] 
tribution of mollusks would lead to the 
hypothesis that South Africa has ever been 
connected with Antarctica and thereby in- 
directly with southern South America.” It is 
finally concluded that “the South American 
mollusean fauna is traceable to two sources: 
an ancient southern continent lying across 
the south Atlantic and enduring from at least 
Paleozoic to near the end of Cretaceous time, 
and to Miocene and Pliocene to recent con- 
nections with the middle American area.” 
Since the appearance of Dr. Pilsbry’s work, 
Dr. Ortmann has published the anatomy of 
the Australian fresh-water mussel Hyridella, 
showing that it is indeed allied to the South 
American Diplodon, further suggesting com- 
munication between these areas. All these 
matters no doubt deserve fuller discussion. 
According to Dr. Schuchert’s recent map, 
North America was rather broadly continuous 
with South in the late Comanchie period, and 
remained so during the Cretaceous. During 
the early and middle Tertiary this connection 
was interrupted; but with the coming of the 
Pliocene, according to Dr. H. F. Osborn, it 
was renewed, and has continued to the present 
day. There should be, therefore, two elements 
in the neotropical fauna, both derived from the 
north, one of Mesozoic age, the other late Ter- 
tiary. The latter is recognized by Dr. Pilsbry, 
but where is the former? Is it not, at least in 
part, the “Eogxic” group of families? Is 
there anything in the Molluscan fauna which 
really supports the idea of a gigantic Gond- 
wana continent, or any other body of land 
crossing the Atlantic or Pacific? It is true 
that molluses are likely to travel slowly, the 
pace of the snail is proverbial; but they are 
ancient and have had time enough. Cochli- 
copa lubrica, assuredly a member of a Pale- 
arctic group, has contrived to crawl all the 
way from the old world to New Mexico within 
the lifetime of its specific type, the animal 
being quite the same in Europe as in Amer- 
ica. There is surely nothing in the distribu- 
tion of snails which might not be explained by 
migrations from the north, and as to the neg- 
ative evidence based on northern palontol- 
ogy, it is clearly not worth much. As Dr. 
Pilsbry truly says, “the rarity of land and 
SCIENCE 
545 
fresh-water shells as fossils, and the great an- 
tiquity of the family groups, renders the ques- 
tion very intricate.” On the other side, there 
is the fact that the Chilinide, certainly of no 
recent origin, have apparently never left 
South America. There are reasons for think- 
ing that in Palxozoic times the Antarctic land 
mass supported a more or less luxuriant flora, 
with a corresponding fauna, which doubtless 
eventually spread in part to other regions of 
the earth* It is even possible that the 
Chilinide came from this source; but we can 
hardly expect to find much, if any, clue to the 
components of this antarctic biota in the pres- 
ent distribution of life, for the simple reason 
that there has been abundant time for it to 
spread over the whole earth, wherever the con- 
ditions permitted. 
Withregard to the northern routefrom South 
America to Africa or Australia, or vice versa, 
it should be clearly understood that it is not 
necessary for a whole fauna to migrate, to ac- 
count for such faunal resemblances as exist. 
Thus the Characinid fishes are to-day abun- 
dantly represented in the Ethiopian and Neo- 
tropical regions, but do not exist elsewhere 
except that one or two species enter the south- 
western part of the nearctic. No fossil 
Characinids have been found in the north. 
The naive conception of a transatlantic bridge: 
on which the Characinids freely traveled ap- 
peals to the imagination, but it is found on 
examination that only one part of the 
African Characinid fauna is really at all close 
to the South American, while the latter has 
very important elements totally diverse from 
the African series. The indications are that 
the Characinids arose in the neotropical, and 
at some very remote period reached Africa, 
where they developed a type (Ichthyoborinz 
+ Distichodontinz, probably to be regarded 
as a distinct family Distichodontide) entirely 
unique in some of its characters. At a much 
later time the Hydrocyonine Characinids ap- 
pear to have arrived in Africa, the immigrants 
consisting perhaps of not more than one or 
two species, which during a relatively brief 
period overran the northern hemisphere, leav- 
1See, for instance, Seward, Quarterly Journal 
Geological Society, August, 1897, pp. 335-338. 
