A. A Ortmann — Climatic zones in Jurassic times. 261 



lived in' former times in cooler water. In this point, I believe, 

 Neumayr's view is incorrect. We are justified in supposing 

 that animals living in cooler water are to be traced back to 

 such ones living in the tropics in former times, that is to say, 

 the adaptation to a cooler climate is a more recent acquisition. 

 But it is very improbable that animals living originally in 

 cooler water migrated back into the tropics, because they 

 would find there a most dangerous concurrence in the struggle 

 of life by the well adapted tropical fauna, while they them- 

 selves were not so well fitted for the tropical conditions. 

 Therefore the stenotherm Reef-corals living nowadays exclu- 

 sively in the tropics and showing no traces of existence in the 

 cooler seas, were most probably stenotherm tropical animals 

 also in former times. If in any groups of animals, we have 

 surely in the Reef-corals sufficient reason for arguing from the 

 recent conditions to the former ones ; especially is this the case 

 in the Mesozoic corals, since these are the direct ancestors of 

 the Tertiary and recent corals. 



II. The pal aeon tological foundations of Neumayr's theory, 

 taken principally from the Ammonites, are the following : 

 The Mediterranean province is characterized by the most 

 general and frequent presence of the genera Phylloceras, 

 Zytoceras, and Simoceras in all the cephalopod-beds, and a 

 very peculiar deposit of this province are the Aptychus-beds. 

 Both the genera just mentioned and the Aptychus-beds are 

 either very rare or wholly wanting in the Middle-European 

 province. The latter, however, shows often a local develop- 

 ment of Sponge-fields and Coral-reefs, connected with the 

 abundance of certain gasteropods, such as JVerinea. On the 

 other hand the genera Oj?j?elia, Peltoceras, Aspidoceras, very 

 frequent in middle Europe, are very rare in the Russian 

 province and the same is the case in the Reef corals. In the 

 latter province again the genus Cardioceras, the group of 

 Belernnites excentricus, and certain bivalves, such as Aucella 

 (Aucella-beds), prevail. 



These differences cannot be overlooked. Nikitin, indeed, 

 attempted to reduce these differences for the Russian Jura, and 

 in some instances, for example as regards the genus Cardio- 

 ceras, he is right (1. c. 1886, p. 232); but his statement, that 

 there prevails an equal fauna throughout the Russian and 

 West-European Jura is at least an exaggeration. According to 

 the lists of fossils given by him, the differences mentioned by 

 Neumayr are certainly present. On the other hand, Nikitin 

 proved the existence of Reef-corals in the Russian province, 

 and although these corals occur only in a few localities, and 

 although JSTeumayr does not notice properly this point in his 



