White Chalk.]
[Illustration: Fig. 196.--_Ostrea Couloni_. Lower Greensand.]
[Illustration: Fig. 197.--_Spondylus spinosus_. White Chalk.]
[Illustration: Fig. 198.--_Inoceramus sulcatus_. Gault.]
The Univalves (_Gasteropods_) of the Cretaceous period are not
very numerous, nor particularly remarkable. Along with species of
the persistent genus _Pleurotomaria_ and the Mesozoic _Nerinoea_,
we meet with examples of such modern types as _Turritella_ and
_Natica_, the Staircase-shells (_Solarium_), the Wentle-traps
(_Scalaria_), the Carrier-shells (_Phorus_), &c. Towards the close
of the Cretaceous period, and especially in such transitional strata
as the Maestricht beds, the Faxoee Limestone, and the Pisolitic
Limestone of France, we meet with a number of carnivorous
("siphonostomatous") Univalves, in which the mouth of the shell is
notched or produced into a canal. Amongst these it is interesting
to recognise examples of such existing genera as the Volutes
(_Voluta_, fig. 200), the Cowries (_Cyproea_), the Mitre-shells
(_Mitra_), the Wing - shells (_Strombus_), the Scorpion-shells
(_Pteroceras_), &c.
[Illustration: Fig. 199.--_Hippurites Toucasiana_. A large
individual, with two smaller ones attached to it. Upper Cretaceous,
South of Europe.]
[Illustration: Fig. 200.--_Voluta elongata_. White Chalk.]
Upon the whole, the most characteristic of all the Cretaceous
Molluscs are the _Cephalopods_, represented by the remains of
both _Tetrabranchiate_ and _Dibranchiate_ forms.
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