346 MR. R. I. POCOCK ON THE [Apr. 21, 
probably be looked to for its ancestry. There seems no reason to 
doubt that it originated in the area it now occupies. 
Families Arypip#, BRACHYBOTHRIIDH, MECICOBOTHRIIDA. 
The genera of Atypide, two in number, scarcely pass south of 
the Equator. Atypus, occurring in the Mediterranean Region, 
and spreading northwards into Central Europe, beyond the 50th 
parallel of north latitude, is the most northern type of the Mygalo- 
morphe. It is also met with in Japan, Burma and Java, and in 
North America, where it ranges to the east of the Mississippi 
from Wisconsin (45th parallel of latitude) to Florida. Calommata 
is more restricted and more southern in range. It is confined to 
the Old World, and has been recorded from Japan, Siam, Burma, 
Sumatra, Java, and the Camaroon area of tropical West Africa. 
The Brachybothriide contain the genera Acattyma from Japan, 
and Brachybothriwm and Atypoides from North America, the latter 
from California, the former from British Columbia, North Carolina, 
Texas, &e. ; 
The Mecicobothriidee comprise two genera—Hexura from the 
two north-western States of North America (Washington and 
Oregon); and MMecicobothrium from the Argentine. 
Atypus seems to be a genus which, like Puchylomerus and others, 
extended in Tertiary times sufticiently far to the north to avail 
itself of the land-connection that then existed across the area 
now covered by the Behring Sea. Its disappearance from the 
countries to the north of its present distributional area must be 
assigned to the refrigeration of this region of the globe with the 
advent of glacial conditions. 
The distribution of Calommata in the eastern part of the 
Oriental Region and in Tropical West Africa has many parallels 
amongst the mammalia, and points to the former extension of the 
genus across an intervening forest-clad tract, and its survival in 
districts where the conditions remained favourable to its existence. 
The explanation given of the distribution of Atypus applies 
equally to the Brachybothriide, except that Atypoides has no 
representative in the Old World. Srachybothrium extends in 
Western America northwards to Queen Charlotte Island, that is 
to say to the latitude of the Aleutian Islands and the Alaska 
Peninsula. Hence its similarity to, perhaps identity with, the 
Japanese Acattyma is no matter for surprise. 
The apparently discontinuous distribution of the Mecico- 
bothriide is very remarkable; but since the only known example 
of Mecicobothriwm measures only 6 mm. in total length, it is 
highly probable that the existence of the genus in South America 
to the north of the Argentine has been overlooked. Considering 
the close structural similarity between Heauwra and Mecicobothrium, 
and the admitted relationship between these two genera and the 
Brachybothriide and Atypide, both northern groups, it seems 
