1903. ] GEOGRAPHICAL DISPRIBUTION OF SPIDERS. 3507 
differences in extremest cases being merely accorded subfamily 
rank and in others only generic rank, it is hard to believe that 
the ancestors of the existing fauna entered South America from 
North America in the early part of the Secondary Period, that is 
to say in pre-Jurassic times, and that they have been isolated since 
that date until the close of the Miocene. Again, if it be supposed 
that they passed southwards from the north after the union of 
the two Americas with the close of the Miocene, the conclusion is 
inevitable either that the wealth of genera now existing in South 
America has been evolved since that date, or that there has been 
such a wholesale destruction of genera in the north as to leave 
but one genus (Aphonopelma) in the Southern States of N, America 
at the present day’. 
The occurrence of this genus in the area in question may be 
equally well attributed to migration of its ancestors northwards 
into the Sonoran Region after the union of North and South 
America at the close of the Miocene. 
Again, since no members of the Aviculariine occur at the 
present time in Australia or Austro-Malaysia, It is needless to 
look to this area as the source of the South-American fauna of 
this subfamily. 
Africa, therefore, and the Mediterranean area alone remain as 
the centres whence the incursion could have taken place. In 
support of the view that preference in this connection should be 
given to Tropical Africa may be urged the following facts. The 
Aviculariine of this region are confined to the forest-region of 
West Africa, which is roughly conterminous with the basin of the 
Congo and includes also the forest-covered district to the north of 
the Gulf of Guinea, and are unknown in South Africa. Secondly, 
the West-African genus Scodra is apparently the nearest living 
ally of the Brazilian genus Avicularia; and Heterothele and 
Solenothele, from the same region as Scodra, are equally nearly 
related, especially the former, to the Patagonian J/itothele. 
Perhaps also some significance must be attached to the cir- 
cumstance that the stridulating-organ which attains such a 
state of perfection in the Kumenophorine is represented in an 
imperfect and unspecialised state in many of the South-American 
genera of Aviculariine. 
Summary of the preceding pages. 
In very early Tertiary times, or, perhaps, still earlier, the primitive 
Macrotheline Dipluride arose in Eastern Asia and spread thence 
in four directions :—(1) South-eastwards into Australia and New 
1 Three other genera, namely Rhechostica, Tapinauchenius, and Avicularia, have 
been recorded from the Southern States of North America; the first from Texas, the 
second from ‘Texas also and * Indian Territory,’ and the third trom California. ‘The 
generic affinities of the first are doubtful; it may indeed be reterable to Aphono- 
pelma. The records of the second and third have little value, since the specimens 
determined were immature females. 
