348 MR. R. I. POCOCK ON THE [ Apr. 21, 
probable that the Mecicobothriide first appeared in North America 
and penetrated thence into South America in the latter half of 
the Tertiary epoch. 
The three families just discussed form an ascending series in 
specialisation, starting with Hexwra, which leads from the 
Dipluride, passing through the Brachybothriide, thence to Atypus, 
and culminating with Calommata, the most specialised of all. 
Assuming, moreover, that dAcattyma and brachybothrium are 
identical, it is noticeable that of the six known genera, three are 
eculiar to the Western (American) hemisphere, two are common 
to both the Eastern and Western, and one only peculiar to the 
Eastern, namely Calommata. In other words, the most primitive 
genera are exclusively American, one that occupies an intermediate 
position (Acattyma) extends only as far as Japan, and the two 
genera of the most specialised Atypide extend from east to west 
throughout the Hastern hemisphere, and one of them, Atypus, to 
the extreme east of the Western hemisphere. 
Since we should expect to find the primitive types of a group 
persisting in the area of its origin and the specialised forms in 
districts remote therefrom, the modifications being brought about 
by the varying conditions of existence incident to wandering, 
North America may be looked upon as the probable home of this 
section of the Mygalomorphe. 
If this be the explanation of their distribution, it presents 
analogies with that of the Camelidee amongst the mammalia, which 
originated in the Sonoran area of America, and thence extended 
into South America and into Central Asia by way of Alaska and 
Kamchatka. 
Family CyRTAUCHENIIDA. 
The genera of Cyrtaucheniide are exceedingly numerous, and 
rival the Dipluride in extent of distribution ; but, owing to the 
complex and puzzling nature of their relationships, it is not easy 
to deduce any satisfactory conclusions from their distribution. 
They are referable to the following sections, which are arranged 
as nearly as possible according to their lines of descent, starting 
with the most primitive, z.e. the Nemesiz, which have departed 
least from the Diplurid type. 
1. Nemesie.—The genus Wemesia itself is abundant in the 
Mediterranean Region, and is met with also in China; Anemesia 
oceurs in Afghanistan, Vemesiellus in 8. India, and Scalidognathus 
in Ceylon. Hermacha, Hermachastes, Lepthereus, Pionothele, and 
Spiroctenus inhabit 8. Africa; Genysa, Madagascar; Arbanitis, 
Australia, Tasmania, and New Zealand; Cantuaria, New Zealand ; 
Rhachias, Carteria, and Hermacha (the last also in 8. Africa) in 
South and Central America. 
2. Cyrtauchenii, differing from Nemesixe in the procurvature 
of the fovea.—Atmetochilus and Damarchus occur in Burma and 
Sumatra; Cyrtauchenius and Amblyocarenum in the Mediter- 
ranean, the latter also in California ; Pelmatorycter in KH. and 8. 
