assic, has recently
been recognised in strata of Carboniferous age in India.

From the foregoing it will be gathered that one of the most important
points in connection with the Triassic _Mollusca_ is the remarkable
intermixture of Palaeozoic and Mesozoic types which they exhibit.
It is to be remembered, also, that this intermixture has hitherto
been recognised, not in the Middle Triassic limestones of the
Muschelkalk, in which--as the oldest Triassic beds with marine
fossils--we should naturally expect to find it, but in the St
Cassian beds, the age of which is considerably later than that
of the Muschelkalk. The intermingling of old and new types of
Shell-fish in the Upper Trias is well brought out in the annexed
table, given by Sir Charles Lyell in his 'Student's Elements of
Geology' (some of the less important forms in the table being
omitted here):--

GENERA OF FOSSIL MOLLUSCA IN THE ST CASSIAN AND HALLSTADT BEDS.

Common to | Characteristic of | Common to
Older Rocks. | Triassic Rocks | Newer Rocks.
| |
Orthoceras. | Ceratites. | Ammonites.
Bactrites. | Cochloceras. | Chemnitzia.
Macrocheilus. | Rhabdoceras. | Cerithium.
Loxonema. | Aulacoceras. | Monodonta.
Holopella. | Naticella. | Sphoera.
Murchisonia. | Platystoma. | Cardita.
Porcellia. | Halobia. | Myoconcha.
Athyris. | Hoernesia. | Hinnites.
Retzia. | Koninckia. | Monotis.
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 e