104 
TH. MORTENSEN 
(Schwed. Südpolar-Exp. 
necting South America with the Kerguelen group and another ridge connecting 
it with the Antarctic Continent, while a great plateau with much shallower water is 
seen to connect the Falkland Islands and South Georgia with South America. 
Whereas we thus have here a very beautiful correspondence between the oceano- 
graphical and the zoogeographical results, such is not to any striking degree the 
case with the supposed connection between South America and Africa. There is a 
distinct mid-Atlantic ridge going from Tristan d’Acunha (which is again in connection 
with the Kerguelen-ridge) northwards to Ascension and then further north to St. 
Paul, the Azores and Iceland. But there can scarcely be said to be distinct indica- 
tions of a former land-bridge from South America to Africa, as wanted by the 
Archhelenis-theory. Judging from the bathymetrical map given by SCHOTT * there 
would be more reason to conclude that both a northern bridge, over Fernando 
Noronha, St. Paul to Guinea, and a southern, from North of La Plata over 
Tristan d’Acunha to Walfish Bay, had existed. In any case the deep West African 
basin does not correspond well with a land connection between the two Continents 
in the extension supposed by IHERING to have existed in the Eocene period. — 
Though, I agree, this is no definite proof against the former existence of the Arch- 
helenis-bridge, it is certainly not in favour of this theory. 
The question of bipolarity among Echinoderms has been so fully discussed that 
it may well be regarded as an established fact that there is no case known of a 
real bipolar species of Echinoderms. (Cf. Echinoiden d. deutschen Südpolar-Expedi- 
tion p. 103 — 104.) Meantime A. H. Clark has quite recently, in a very interesting 
paper »The recent Crinoids and their relation to Sea and Land» (The Geographical 
Journal 1908, p. 602) established a »Polar-Pacific» region (or fauna), »embracing the 
Arctic and Antarctic Seas, and the entire Pacific Coast of North and South Ame- 
rica». »The unstalked Crinoids occurring here belong exclusively to the Antedonidæ; 
Helionietra occurs everywhere; Thaumatometra and Isometra are found in the Ant- 
arctic section only, and Hathrometra only in the Arctic.» The main reason for 
uniting both antarctic and arctic sea into one »Fauna» is evidently the occurrence of 
the genus Helionietra in both. I am not going to enter in a more detailed manner 
upon this matter, I would only point out that the Echinoids decidedly bear no 
evidence for the connection between the antarctic and the arctic fauna. The Echi- 
noid fauna of the Patagonian-Chilian region does not reach the Gulf of Panama 
(the alleged occurrence of Anstrocidaris canaliculata at Altata is evidently wrong, 
cf. above p. 20), and there is no nearer relation whatever between the Echinoid 
faunas of the North American and the South American Pacific Coast. 
* Gerh. Schott, Océanographie u. maritime Meteorologie. Wissenseh. Ergehn, d. deutschen Tiefsee- 
Exped. I. 1902. 
