Fig. 397: Equisetites columnaris. _St. Cassian and Hallstadt Beds_ (see Map, Fig. 398).— The sandstones and clay of the Keuper resemble the deposits of estuaries and a shallow sea near the land, and afford, in the N.W. of Germany, as in France and England, but a scanty representation of the marine life of that period. We might, however, have anticipated, from its rich reptilian fauna, that the contemporaneous inhabitants of the sea of the Keuper period would be very numerous, should we ever have an opportunity of bringing their remains to light. This, it is believed, has at length been accomplished, by the position now assigned to certain Alpine rocks called the “St. Cassian beds,” the true place of which in the series was until lately a subject of much doubt and discussion. It has been proved that the Hallstadt beds on the northern flanks of the Austrian Alps correspond in age with the St. Cassian beds on their southern declivity, and the Austrian geologists, M. Suess of Vienna and others, have satisfied themselves that the Hallstadt formation is referable to the period of the Upper Trias. Assuming this conclusion to be correct, we become acquainted suddenly and unexpectedly with a rich marine fauna belonging to a period previously believed to be very barren of organic remains, because in England, France, and Northern Germany the upper Trias is chiefly represented by beds of fresh or brackish water origin. Fig. 398: Map of Tyrol and Styria showing St. Cassian and Hallstadt Beds. Fig. 399: Scoliotoma. Fig. 400: Koninckia Leonhardi. About 600 species of invertebrate fossils occur in the Hallstadt and St. Cassian beds, many of which are still undescribed; some of the Mollusca are of new and peculiar genera, as _Scoliostoma,_ Fig. 399, and _Platystoma,_ Fig. 400, among the Gasteropoda; and _Koninckia,_ Fig. 401, among the Brachiopoda. Fig. 401: Koninckia Leonhardi. The following table of genera of marine shells from the Hallstadt and St. Cassian beds, drawn up first on the joint authority of M. Suess and the late Dr. Woodward, and since corrected by Messrs. Etheridge and Tate, shows how many connecting links between the fauna of primary and secondary Palæozoic and Mesozoic rocks are supplied by the St. Cassian and Hallstadt beds. GENERA OF FOSSIL MOLLUSCA IN THE ST. CASSIAN AND HALLSTADT BEDS. Common to Older Rocks Characteristic Triassic Genera Common to Newer Rocks Orthoceras Bactrites Macrocheilus Loxonema Holopella Murchisonia Porcellia Athyris Retzia Cyrtina Euomphalus Ceratites Cochloceras Choristoceras Rhabdoceras Aulacoceras Scoliostoma [5] Naticella Platystoma Ptychostoma Euchrysalis Halobia Hornesia Amphiclina Koninckia Cassianella [6] Myophoria [6] Ammonites Chemnitzia Cerithium Monodonta Opis Sphoera Cardita Myoconcha Hinnites Monotis Plicatula Pachyrisma Thecidium