1911.] Proceedings of the Asiatic Society of Bengal. CXXV 
found here are of the most highly specialized type. Species of 
Thelyphonus belonging to this most highly specialized type are 
dominant in the Malay Peninsular and Siam also, though here 
they are much fewer in number, but nowhere else unless it be 
in the Philippines. The further one looks from the neigh- 
bourhood of Borneo, however, the more frequently are less 
specialized forms met with, the least specialized of all being 
dominant only in Ceylon, the Indian Peninsular, the Eastern 
Himalayas, Assam, and Eastern China to the west and north, 
and in South America to the east; whilst a species specialized 
in an intermediate degree is dominant in the Liu Kiu 
Islands and Japan to the north-east; these being the limits 
of distribution of the family. This arrangement in what may 
as more highly specialized forms were evolved the simpler 
ones were pushed further and further outwards. 
The distribution of those Thelyphonidae which are distin- 
guished from the ones already dealt with by the absence of 
ridges at the sides of the head between the median and lateral 
eyes, suggests that these were originally centred in much the 
same place as the others, and that they have been entirely 
pushed outwards by them; for they are now known with 
certainty only in the moister parts of Ceylon and the west 
coast of India, in and around Burma, and in 8. America. 
When the migrations resulting in the present distribution of 
the family commenced therefore, the prototypes of the two 
principal divisions into which the Thelyphonidae naturally fall 
appear to have been already distinct from one another; and, 
from the minuteness with which (at most) any Thelyphonid 
species or groups of species. eir o rende 
highly probable by the fact that the closely allied Geralinuridae 
occur in the Coal Measures of Britain. The two prototypes 
of the Thelyphonidae as we know them to-day were probably 
therefore members of a more extensive group the rest of which 
