Cyrtina. | Scoliostoma. | Plicatula.
Euomphalus. | Myophoria. | Pachyrisma.
|(The last two are | Thecidium.
|principally but not |
|exclusively Triassic.)|
Thus, to emphasise the more important points alone, the Trias
has yielded, amongst the Gasteropods, the characteristically
Palaeozoic _Loxonema, Holopella, Murchisonia, Euomphalus_, and
_Porcellia_, along with typically Triassic forms like _Platystoma_
and _Scoliostoma_, and the great modern groups _Chemnitzia_ and
_Cerithium_. Amongst the Bivalves we find the Palaeozoic _Megalodon_
side by side with the Triassic _Halobia_ and _Myophoria_, these
being associated with the _Carditoe, Hinnites, Plicatuloe_, and
_Trigonioe_ of later deposits. The Brachiopods exhibit the Palaeozoic
_Athyris, Retzia_, and _Cyrtina_, with the Triassic _Koninckia_
and the modern _Thecidium_. Finally, it is here that the ancient
genera _Orthoceras, Cyrtoceras_, and _Goniatites_ make their last
appearance upon the scene of life, the place of the last of these
being taken by the more complex and almost exclusively Triassic
_Ceratites_, whilst the still more complex genus _Ammonites_ first
appears here in force, and is never again wanting till we reach
the close of the Mesozoic period.
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