that is, on the ascending side) are
Limulus and the Eurypterines--with a long gap, due to obliteration of
the record, separating them from the trilobite. On the other
side--tending downwards from the scorpion towards the Acari--are the
Pedipalpi, the spiders, the book-scorpions, the harvest-men and the
water-mites.

The strange nobody-crabs or Pycnogonids occupy a place on the ascending
half of the arc below the Eurypterines and Limulus. They are strangely
modified and degenerate, but seem to be (as explained in the systematic
review) the remnant of an Arachnidan group holding the same relation to
the scorpions which the Laemodipoda hold to the Podophthalmate
Crustacea.

* * * * *

We have now to offer a classification of the Arachnida and to pass in
review the larger groups, with a brief statement of their structural
characteristics.

In the bibliography at the close of this article (referred to by leaded
arabic numerals in brackets throughout these pages), the titles of works
are given which contain detailed information as to the genera and
species of each order or sub-order, their geographical distribution and
their habits and economy so far as they have been ascertained. The
limits of space do not permit of a fuller treatment of those matters
here.

TABULAR CLASSIFICATION[6] OF THE ARACHNIDA.

CLASS. ARACHNIDA.

_Grade A. ANOMOMERISTICA._
Sub-Class. TRILOBITAE.
Orders. Not satisfactorily determined.

_Grade B. NOMOMERISTICA._
Sub-Class I. PANTOPODA.
Order 1. Nymphonomorpha.
" 2. Ascorhynchomorpha.
" 3. Pycnogonomorpha.
Sub-Class II. EU-ARACHNIDA.
Grade a. DELOBRANCHIA, Lankester (_vel_ HYDROPNEUSTEA, Pocock).
Order 1. Xiphosura.
" 2. Gigantostraca.
Grade b. EMBOLOBRANCHIA, Lankester (_vel_ AEROPNEUSTEA, Pocock).
_Section_ [alpha]. _Pectinifera._
Order 1. Scorpionidea.
Sub-order a. Apoxypoda.
" b. Dionychopoda.
_Section_ [beta]. _Epectinata._
Order 2. Pedipalpi.
Sub-order a. Uropygi.
Tribe 1. Urotricha.
" 2. Tartarides.
Sub-order b. Amblypygi.
Order 3. Araneae.
Sub-order a. Mesothelae.
" b. Opisthothelae.
Tribe 1. Mygalomorphae.