respects so entirely different, should, like
_Ichthyornis_ and _Hesperornis_, have lived not only in the same
geological period, but also in the same geographical area; and
it is equally curious that the area inhabited by these toothed
Birds should at the same time have been tenanted by winged and
bird-like Reptiles belonging to the toothed genus _Pterodactylus_
and the toothless genus _Pteranodon_.

[Illustration: Fig. 212.--Toothed Birds (_Odontornithes_) of the
Cretaceous Rocks of America. a. Left lower jaw of _Ichthyornis
dispar_, slightly enlarged; b, Left lower jaw of _Hesperornis
regalis_, reduced to nearly one-fourth of the natural size; c.
Cervical vertebra of _Ichthyornis dispar_, front view, twice
the natural size; c', Side view of the same; d, Tooth of
_Hesperornis regalis_, enlarged to twice the natural size. (After
Marsh.)]

No remains of _Mammals_, finally, have as yet been detected in
any sedimentary accumulations of Cretaceous age.

LITERATURE.

The following list comprises some of the more important works and
memoirs which may be consulted with reference to the Cretaceous
strata and their fossil contents:--

(1) 'Memoirs of the Geological Survey of Great Britain.'
(2) 'Geology of England and Wales.' Conybeare and Phillips.
(3) 'Geology of Yorkshire,' vol. ii. Phillips.
(4) 'Geology of Oxford and the Thames Valley.' Phillips.
(5) 'Geological Excursions through the Isle of Wight.' Mantell.
(6) 'Geology of Sussex.' Mantell.
(7) 'Report on Londonderry,' &c. Portlock.
(8) 'Recherches sur le Terrain Cretace Superieur de l'Angleterre
et de l'Irlande.' Barrois.
(9) "Geological Survey of Canada"--'Report of Progress, 1872-73.'
(10) 'Geological Survey of California.' Whitney.
(11) 'Geological Survey of Montana, Idaho, Wyoming, and Utah.'
Hayden and Meek.
(12) 'Report on Geology,' &c. (British North American Boundary
Commission). G. M. Dawson.
(13) 'Manual of Geology.' Dana.
(14) 'Lethaea Rossica.' Eichwald.
(15) 'Petrefacta Germaniae.' Goldfuss.
(16) 'Fossils of the South Downs.' Mantell.
(17) 'Medals of Creation.' Mantell.
(18) 'Mineral Conchology.' Sowerby.
(19) 'Lethaea Geognostica.' Bronn.
(20) 'Malacostracous Crustacea of the British Cretaceous Formation'
(Palaeontographical Society). Bell.
(21) 'Brachiopoda of the Cretaceous Formation' (Palaeontographical
Society). Davidson.
(22) 'Corals of the Cretaceous Formation' (Palaeontographical
Society). Miln