Page:A Treatise on Geology, volume 1.djvu/99

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CH. V.
ORGANIC REMAINS OF PLANTS AND ANIMALS.
83



Table II.—Genera Containing many Fossil Species.(conchifera.)

Producta Spiri-
fera
Tere-
bratula
Trigonia Phola-
domya
Plagi-
ostoma
Inoce-
ramita
Gryphæa
Living species 15 1 1 1
In Cainozoic strata 18 1 1
In Mesozoic strata 6 106 33 19 38 20 24
In Palaeozoic strata 64 90 65 10


The unequal periods of existence of different genera are here very apparent. Producta, after abounding in Devonian and carboniferous ages, perishes in the saliferous period. Spirifera passes through all these periods and ends in the oolitic; but terebratula occurs through all the strata, and still lives.


Table III.—Genera of Cephalopoda.

Belle-
rophon
Ortho-
ceras
Belem-
nites
Nautilus Ammo-
nites
Hamites Scaphites Baculites Nummu-
lites
Living species 2
In Cainozoic strata 4 ? 3
In Mesozoic strata 83 22 221 30 5 5
In Palaeozoic strata 24 57 31 53


Most of the fossil cephalopoda belong to extinct genera: of these, bellerophon and orthoceras are abundant in the lower and middle palaeozoic strata. Hamites, scaphites (almost peculiar to the cretaceous system, a few only in the oolites), and Belemnites, belong to the mesozoic series, and characterise the oolitic and chalk rocks exclusively.