BIOLOGIA CENTRALI-AMERICANA. 
ZOOLOGIA. 
Class ARACHNIDA. 
Order ARANEIDEA. 
Suborder OPISTHOTHELZ, Pocock. 
Section MYGALOMORPH &, Pocock. 
The Mygalomorphe include all the spiders which possess four distinct lung-sacs as 
distinct from two lung-sacs and two tracheal stigmata of the Dysderide, &c., or two 
lung-sacs and one tracheal stigma of the other Arachnomorphe. 
Both in the number of lung-sacs retained, in the disposition of the spinning-mamille, 
and in the plane of the articulation of the mandibles, these spiders exhibit characters 
which suggest archaic arachnidal forms, of which Liphistius is perhaps the sole 
surviving link. In the Arachnomorphe the second pair of lung-sacs have become 
tracheal stigmata and the plane of articulation of the mandibles has become oblique 
instead of horizontal, while the spinning-mamille, having achieved the utmost 
possible degree of distal migration, assume a closely grouped position at the apex of 
the abdomen. 
So far as regards the distribution of the Mygalomorphe over the earth’s surface, 
one may say that, roughly speaking, they occupy the broad zone which lies 
between the fortieth parallel north and south of the Equator. The family Atypide, 
however, occurs much further north, extending almost up to the sixtieth parallel. 
Members of the family Ctenizide and also of the Dipluride extend further both 
in a northerly and southerly direction than do those of the family Theraphoside 
as defined in the present work, while along the northern shores of the Mediterranean 
numerous species of the former family occur where the latter is but feebly represented. 
The Theraphoside, which include the largest known species, some of them measuring 
9 inches in expanse of limbs, occur throughout Africa, Arabia, Hindostan, Burmah, 
Sumatra, Java, New Guinea, and other adjacent islands, and the east coast of Australia. 
In the Neotropical region they occur in the Southern States of North America, in 
BIOL. CENTR.-AMER., Arachn. Aran., Vol. II., August 1897. BE 
