TRIASSIC PERIOD. 429 



Coprolites of Reptiles are also common. 



(d.) Mammals. — Fig. 753 represents the side-view of a tooth of Microlestes antiquus 

 Plien., from the bone-breccia of Wurtemberg. A tooth of the same species was found 

 at Frome, England. Owen regards the species as probably near the modern Myrme- 

 cobius, and closely related to another extinct Marsupial, Plagiaulax, of the English Up- 

 per Oolyte. Fig. 753 a shows the crown of the tooth. 



Fossils characteristic of the subdivisions of the Trias. — The following are character- 

 istic fossils of the three subdivisions of the Trias: — 



1. Lower group. — Voltzia heterophylla, Calamites Mougeoti L. & H. Neuropteris 

 elegans Brngt. ; Placodus impressus Ag. ; Nothosaurus Schimperi Mey. ; Trematosaurus ; 

 footprints of Labyrinthodonts. 



2. Middle group. — Encrinus liliiformis, Gervillia socialis Qu. (common to all the 

 groups), Myophoria (Trigonia) vulgaris Br., M. lineata Mii., Terebratula vulgaris, 

 Ceratites nodosus, Nautilus bidorsatus Br., Pemphix Sueurii ; Hybodus Mougeoti Ag., H. 

 major Ag., Placodus (several species) ; Nothosaurus (species differing from those of the 

 lower group), Simosaurus, Pistosaurus. 



3. Upper group, or Keuper. — Equiseta, Calamites arenaceus Jag., Pterophyllum 

 Jageri Brngt., Pt. longifolium Brngt., PL (Pterozamites) Miinsteri Gopp., Mastodon* 

 saurus giganteus, Belodon, Termatosaurus ; Microlestes antiquus. 



The Estheria minuta ranges through all the divisions. 



The St. Cassian beds contain species of the Paleozoic genera Orthoceras (seven or eight 

 species), Cyrtoceras, Gonhtitcs, Loxonema, Holopella, Murchisonia, Evomphalus, Porcellia 

 (Bellerophon), Megalod<-n, Cyrtia, which are not known afterward, along with others 

 peculiarly Triassic, such as Monotis salinaria Br., Halobia Lommeli Wiss., Myophoriw, 

 Ammonites. The Dachstein beds contain, among their fossils, Megalodon triqueter Wulf., 

 Avicula intermedia Emmr., Spirifer Miinsteri Dav., Sp. rostratus Schloth., Terebratula 

 cornuta Sow., T. pyriformis Suess, T. gregaria Suess, Rhynchonella cornigera Schafh., 

 The Kbssen beds have afforded an Orthoceras, a Belemnite, Ammonites trisulcatus Brngt , 

 Pleurotomaria expansa Goldf., Megalodon triqueter Wulf., Gervillia inflata Schafh., 

 Avicula contorta Portl., A. inmquivalcis Sow., Lima gigantea Sow., Pinna folium Phil., 

 Cardium Rhmticum Merian, Hemicardium Wulfeni, Pecten liasinus Nyst., Pecten Valo- 

 niensis Defr., Lithostrotion, etc. 



The Rhaetic beds in England contain Avicula contorta, Pecten Valoniensis Defr. 

 (these two species characteristic and abundant), A. incequ/valvis, Cardium Rhaiticum, 

 Pullastra arenicola Strickl., Monotis decussata Mii., Modiola minima Sow., Ostrea lias- 

 ska Strickl.; Sjnrifer Miinsteri, Estheria minuta ; Acrodus minimus Ag., Hybodus pli- 

 catilis, Saurichthys apicalis Ag., Gyrolepis tenuistriatus Ag., vertebrae of Ichthysosaurs 

 and Plesiosaurs, tracks of Cheirotherium; teeth of Microlestes (at Frome). Many of the 

 species occur also in the Lias. 



The Triassic rocks of Spitzbergen, partly bituminous shales, have afforded species of 

 Nautilus, Ammonites, Ceratites, Halobia, etc., closely like, if not identical with, species 

 of the St. Cassian beds (Laube). 



3. General Observations on the Trias. 



Life of the Period. — The steps of progress in the life of the 

 globe, as the Mesozoic era opened in the Triassic period, were espe- 

 cially important. The storing away of the excess of atmospheric 

 carbon, as coal, had purified the atmosphere ; and, soon after the close 

 of Paleozoic time — whose great feature was that its animal life had 

 made rocks, and its plants, coal — there were higher races breathing 

 the better air. Saurians became numerous ; and the vertebrate type 

 expanded by the appearance of species of the new class of Mammals 



