ARACHNIDA. 123 
The distribution of the Diplocentrine is still more remarkable. Four genera belong 
to this subfamily, two being American and two Arabian. In addition to Diplocentrus *, 
the range of which has already been stated, America contains the well-marked genus 
Oiclus, known hitherto only from Antigua in the Lesser Antilles. The Arabian genera 
are Nebo recorded from Syria and Arabia and Heteronebo discovered in the island 
of Abd-el-Kuri by Sokotra. This singular discontinuity in distribution is closely 
paralleled by that of the Centipede Scolopendra (see p. 134). To explain it one may 
tentatively suggest a transatlantic connection between the Mediterranean area of 
Europe and America by way of the Antilles, an hypothesis supported by the survival 
of Scolopendra in the Canary Islands. Assuming this to be the explanation, it is 
probable that America received its Diplocentrine Scorpions from the Mediterranean 
area, and not vice versd, because the Old World, and not the New World, is at the 
present time the home of the Scorpionide, to which the Diplocentrine belong. 
Very little can be said about the origin of the remaining Central American genera. 
The absence of the Vejovide from tropical Africa eliminates the latter country as a 
possible source for this family. Its mainly. extratropical range in the Old World, 
coupled with its existence at the present time in North America, suggests its former 
wide distribution in the Northern Hemisphere; and possibly the break in the 
distribution of the Vejovine in America, above alluded to, points to the southward 
migration of the family from the western parts of North America to the western parts 
of South America before the elevation of the isthmus of Panama. In this connection 
the absence of the family from the Antilles is significant. 
The dominance of the Buthide in the Old World as compared with the New 
World suggests the Old World as the original home of the family; but whether the 
ancestors of the American genera entered America by a transatlantic bridge from 
Africa or Europe or by the known eastern or western northern routes under tropical 
or warm temperate conditions, it is impossible to say. 
REGIONAL AND SUBREGIONAL DISTRIBUTION OF AMERICAN SCORPIONS. 
Making allowances for incomplete knowledge, which renders accurate mapping of 
boundaries impossible, it seems that America may be divided by its Scorpions into the 
same geographical areas as those indicated by the Mammalia. ‘The northern parts 
of the continent to the north, roughly speaking, of the 40th parallel agree with the 
corresponding areas of the Old World in being without Scorpions. This negative 
feature defines the Holarctic Region. Sharply distinguished from this by the 
presence of Scorpions are the Southern States of the Union ; and the extension of two 
of the genera (Hadrurus, Vejovis) into Mexico, but no farther, affiliates the greater part 
* Including Didymocentrus, Kraepelin. 
R2 
