the Purbeck beds of Swanage, and the vales of
Wardour and Aylesbury, in the Stonesfield Slate series, and in the Lias
and Rhaetic series of the west of England. But the richest strata appear
to be those of the Upper Miocene at Oeningen, near Schaffhausen in the
Rhine valley; the Middle Miocene at Radaboj, near Krapina in Croatia;
the Eocene of Aix, in Provence; and more especially the celebrated
Secondary rocks furnishing the lithographic stone of Solenhofen, in
Bavaria. This latter deposit would appear to have been of marine origin,
and it is significant that, although the remains of gigantic
dragon-flies discovered in it are very numerous and perfect, no traces
of their subaquatic conditions have been found, although these as a rule
are numerous in most of the other strata, hence the insects may be
regarded as having been drowned in the sea and washed on shore. Many of
these Solenhofen species differ considerably in form from those now
existing, so that Dr H. A. L. Hagen, who has especially studied them,
says that for nearly all it is necessary to make new genera. It is of
great interest, however, to find that a living Malayan genus (_Euphaea_)
and another living genus _Uropetala_, now confined to New Zealand, are
represented in the Solenhofen deposits, while a species of
_Megapodagrion_ now entirely Neotropical, occurs in the Eocene beds of
Wyoming.

A notice of fossil forms should not be concluded without the remark that
indications of at least two species have been found in amber, a number
disproportionately small if compared with other insects entombed
therein; but it must be remembered that a dragon-fly is, as a rule, an
insect of great power, and in all probability those then existing were
able to extricate themselves if accidentally entangled in the resin.

See E. de Selys-Longchamps, _Monographie des Libellulidees d'Europe_
(Brussels, 1840); _Synopses des Agrionines, Calopterygines, Gomphines,
et Cordulines_, with Supplements (Brussels, from 1853 to 1877); E. de
Selys-Longchamps and H. A. L. Hagen, _Revue des Odonates d'Europe_
(Brussels, 1850); _Monographie des Calopterygines et des Gomphines_
(Brussels, 1854 and 1858); Charpentier, _Libellulinae europeae_
(Leipzig, 1840). For modern systematic work see various papers by R.
M'Lachlan, P. P. Calvert, J. G. Needham, R. Martin, E. B. Williamson,
F. Karsch, &c.; also H. Tumpel, _Die Geradflugler Mitteleuropas_
(Eisenach, 1900); and W. F. Kir