Fig. 81.—Ceratites nodosus. (Muschelkalk.)
Among the shells characteristic of the Muschelkalk period, we mention Natica Gaillardoti, Rostellaria antiqua, Lima striata, Avicula socialis, Terebratula vulgaris, Turbonilla dubia, Myophoria vulgaris, Nautilus hexagonalis, and Ceratites nodosus. The Ceratites, of which a species is here represented ([Fig. 81]), form a genus closely allied to the Ammonites, which seem to have played such an important part in the ancient seas, but which have no existence in those of our era, either in species or even in genus. This Ceratite is found in the Muschelkalk of Germany, a formation which has no equivalent in England, but which is a compact greyish limestone underlying the saliferous rocks in Germany, and including beds of dolomite with gypsum and rock-salt.
The Mytilus or Mussel, which properly belonged to this age, are acephalous (or headless) Molluscs with elongated triangular shells, of which there are many species found in our existing seas. Lima, Myophoria, Posidonia, and Avicula, are acephalous Molluscs of the same period. The two genera Natica and Rostellaria belong to the Gasteropoda, and are abundant in the Muschelkalk in France, Germany, and Poland.
Fig. 82.—Encrinus liliiformis.
Among the Echinoderms belonging to this period may be mentioned Encrinus moniliformis and E. liliiformis, or lily encrinite ([Fig. 82]), whose remains, constituting in some localities whole beds of rock, show the slow progress with which this zoophyte formed beds of limestone in the clear seas of the period. To these may be added, among the Mollusca, Avicula subcostata and Myophoria vulgaris.
In the Muschelkalk are found the skull and teeth of Placodus gigas, a reptile which was originally placed by Agassiz among the class of Fishes; but more perfect specimens have satisfied Professor Owen that it was a Saurian Reptile.
It may be added, that the presence of a few genera, peculiar to the Primary epoch, which entirely disappeared during the sub-period, and the appearance for the first time of some other animals peculiar to the Jurassic period, give to the Muschelkalk fauna the appearance of being one of passage from one period to the other.