ST. CASSIAN AND HALLSTADT BEDS. 
377 
Assuming this conclusion to be correct, we become acquainted 
suddenly and unexpectedly with a rich 
marine fauna belonaino’ to a period j^re- 
Fiff. 399. 
viously believed 
very barren of 
remains, because 
to be 
organic 
in Eng- 
Fio-. 400. 
Scoliostoma, St. Cassiaii. 
Platysto7na Suessiif 
Horne.-. From 
Hallstadt. 
Fm. 401. 
land, France, and North¬ 
ern Germany the upper 
Trias is chiefly represent¬ 
ed by beds of fresh or 
brackish water origin. 
About 600 species of invertebrate fossils occur in the Hall¬ 
stadt and St. Cassian beds, many of which are still unde¬ 
scribed ; some of the 
Mollusca are of new 
and peculiar genera, as 
Scoliostoma, Fig. 399, 
and Platystoma. Fig. 
400, among the Gaster¬ 
opoda ; and Koninckia, 
Fig. 401, among the 
Brachiopoda. 
The following table 
of genera of marine 
shells from the Hall¬ 
stadt 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 Palaeozoic and Mesozoic rocks are supplied 
by the St. Cassian and Hallstadt beds. 
Koninckia LconUardi, Wissmanii. 
a. Ventral view. Part of ventral valve removed to 
show the vascular impressions of dorsal valve, 
fe. Interior of dorsal valve, showing spiral proc¬ 
esses restored, c. Vertical section of both valves. 
Part shaded black showing place occupied by the 
animal, and the dorsal valve following the curve 
of the ventral. 
GENERA OF FOSSIL MOLLUSCA IN THE ST. CASSIAN AND HALLSTADT BEDS. 
Common to Older Rocks. 
Orthoceras. 
Bactrites. 
Macrocheilus. 
Loxonema. 
Holopella. 
Murchisonia. 
Porcellia. 
Athyris. 
Retzia. 
Cyrtina. 
Euomphaliis. 
) Characteristic Triassic Genera. 
Ceratites. 
Cochloceras. 
Choristoceras. 
Rhabdoceras. 
Aulacoceras. 
* Scoliostoma. 
Naticella. 
Platystoma. 
Ptychostoraa. 
Euchrysalis. 
Halobia. 
Hbrnesia. 
Amphiclina. 
Koninckia. 
** Cassianella. 
** Myophoria. 
Common to Newer Rocks. 
Ammonites. 
Cheinnitzia. 
Cerithium. 
Monodonta. 
Opis. 
Sphoera. 
Cardita. 
Myoconcha. 
Hinnites. 
Monotis. 
Plicatula. 
Pachyrisma. 
Thecidium. 
* Reaches its maximum in the Trias, but passes down to older rocks. 
Reach their maximum in the Trias, but pass up to newer rocks. 
