LIBRARY

EPHEMERIDA 226
most important genera are: Siphlonurus 1 Eaton (Holarctic), Ameletus Eaton
(Holarctic, Australian), Chirotonetes Eaton (Nearctic), Siphlonisca Needham
(Nearctic), Siphlurella Bengtsson (Palrearctic), Isonychia Eaton (Holarctic),
Oniscigaster McLachlan (Indo.Australian), and Coloburiscus Eaton (Austra.
lian).
Ameletus ornatus Eaton of New Zealand is remarkable in that the nymphs
crawl out of the water on the damp rocks near or in the spray of waterfalls and
cascades and jump back into the water when disturbed. A. perdtus Eaton,
another large New Zealand species, is carnivorous.
Family BlETISCIDlE Ulmer 1920 (Bre-tis'ci-dre, see R£TIDiE for derivation).
The eastern American species, B;:etisca obesa Walsh, will serve as a representative
of this family. The naiad is peculiar and is described by Needham
as having a huge four-spined carapace formed by a backward prolongation of
the thoracic notum which meets a conspicuous pyramidal elevation on the
middle of the abdomen to enclose a respiratory chamber within which the gills
are included.
It is a rare species thought to inhabit the rapid waters of larger rivers.
The male subimago has partly clouded wings whereas the imago has hyaline
wings.
Family PROSOPISTOMATIDlE Lestage 1919 (Pro'so·pis'to-mat'i-d