tained as organs subservient to reproduction or silk-spinning. Mouth
situated more forwards than in Delobranchia, no share in mastication
being taken by the basal segments of the 5th and 6th pairs of
prosomatic appendages. Lateral eyes, when present, represented by
separate ocelli.

The prae-genital somite, after appearing in the embryo, either is
obliterated (_Scorpio, Galeodes, Opilio_and others) or is retained as
a reduced narrow region of the body, the "waist," between prosoma and
mesosoma. It is represented by a full-sized tergal plate in the
Pseudo-scorpiones.

Section [alpha]. _Pectinifera._--The primitive distinction between the
mesosoma and the metasoma retained, the latter consisting of six
somites and the former of six somites in the adult, each of which is
furnished during growth with a pair of appendages. Including the
prae-genital somite (fig. 16), which is suppressed in the adult, there
are thirteen somites behind the prosoma. The appendages of the 1st and
2nd mesosomatic somites persisting as the genital operculum and
pectones respectively, those of the 3rd, 4th, 5th and 6th somites (?
in _Palaeophonus_) sinking below the surface during growth in
connexion with the formation of the four pairs of pulmonary sacs (see
fig. 17). Lateral eyes monostichous.

[Illustration: Restored after Thorell's indications by R.I. Pocock.

FIG. 48.--Dorsal view of a restoration of _Palaeophonus nuncius_,
Thorell. The Silurian scorpion from Gothland.]

Order 1. Scorpiones.--Prosoma covered by a single dorsal shield,
bearing typically median and lateral eyes; its sternal elements
reduced to a single plate lodged between or behind the basal segments
of the 5th and 6th pairs of appendages. Appendages of 1st pair
tri-segmented, chelate; of 2nd pair chelate, with their basal segments
subserving mastication; of 3rd, 4th, 5th and 6th pairs similar in form
and function, except that in recent and Carboniferous forms the basal
segments of the 3rd and 4th are provided with sterno-coxal (maxillary)
lobes, those of the 4th pair meeting in the middle line and underlying
the mouth. The five posterior somites of the metasoma constricted to
form a "tail," the post-anal sclerite persisting as a weapon of
offence and provided with a pair of poison glands (see figs. 8, 10,
12, 13, 14, 15, 21 and 22).

Sub-order Apoxypoda.--The 3rd, 4th, 5th and 6th pairs of appendag