s, the reader is referred to the works of M'Cook (30)
and the Peckhams (31), whilst an excellent account of the nests of
trap-door spiders is given by Moggridge (32). References to systematic
works will also be found at the end of this article (33).

Order 4. Palpigradi = Microthelyphonidae (see fig. 65).--Prosoma
covered above by three plates, a larger representing the dorsal
elements of the first four somites, and two smaller representing the
dorsal elements of the 5th and 6th.

Its ventral surface provided with one prosternal, two mesosternal and
one metasternal plate. Appendages of 1st pair consisting of three
segments, completely chelate, without poison gland; of 2nd pair
slender, leg-like, tipped with three claws, the basal segment without
sterno-coxal process taking no share in mastication, and widely
separated from its fellow of the opposite side; 3rd, 4th, 5th and 6th
appendages similar in form to the 2nd and to each other.

Proboscis free, not supported from below by either the prosternum or
the basal segments of the appendages of the 2nd pair.

[Illustration: FIG. 65.--_Koenenia mirabilis_, Grassi, one of the
Palpigradi.

A, Ventral view of prosoma and anterior region of opisthosoma with
the appendages cut off near the base; a and b, prosternites; c,
mesosternite; and d, metasternite of the prosoma; f, ventral
surface of the prae-genital somite; g, sternite of the genital
somite (first opisthosomatic somite).
B, Dorsal view. I to VI, prosomatic appendages; 1 opisth, genital
somite (first opisthosomatic somite).
C, Lateral view, I to VI, prosomatic appendages; a, b, c, the three
tergal plates of the prosoma; prae-gen, the prae-genital somite; 1
to 10, the ten somites of the opisthosoma.
D, Chelicera.

(Original drawing by Pocock and Pickard-Cambridge, after Hansen and
Sorensen.)]

Opisthosoma consisting of only ten somites, which have no tergal and
sternal elements, the prae-genital somite contracted to form a
"waist," as in the Pedipalpi; the last three narrowed to form a caudal
support for the many-jointed flagelliform telson, as in the Urotricha.
Respiratory organs atrophied.

Family--Koeneniidae (_Koenenia_).

_Remarks._--An extremely remarkable minute form originally described
by Grassi (34) from Sicily, and since further described by Hansen
(35). Recently the genus has been fo