412 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



Session of Wednesday, August 4 



The meeting was called to order by Prof. J. P. Smith at 2.30 o'clock, 

 ill room 320, Department of Geology, Stanford University. Prof. J. C. 

 Merriam was then called to the chair. The symposium, "Correlation of 

 the Triassic," formed the topic for this meeting, and four following 

 papers on this subject were presented : 



RELATIONS OF THE INVERTEBRATE FAUNAS OF THE AMERICAN TRIASSIC 



to those of asia and europe 



by james perrin smith 



Discussion 



In answ^er to a query by Professor Merriam as to the number of species 

 occurring in the Triassic of California, Professor Smith replied that a con- 

 servative estimate would place the number at about 400. He stated that the 

 number of interregional faunas were three in the Lower, two In the Middle, 

 and four in the Upper Triassic. These are separated by local faunas. In 

 Europe definite faunal zones can be recognized, and between these are beds 

 not characteristically fossil if erous, or in some cases non-fossiliferous. 



In reply to Professor Merriam's (luery as to whether these interregional 

 faunas were more or less common in the Triassic than in later periods. Pro- 

 fessor Smith replied that they were much more common in the Triassic. 



Professor Schuchert emphasized the cosmopolitan range of ammonites, 

 their extensive migration, and stated that there was nothing comparable among 

 the other groups of invertebrates. 



Professor Smith stated that the ammonites were apparently exceedingly 

 sensitive to changes in their diet. They appear to be represented about coral 

 reefs and are not foiuid in black shales. 



Doctor Ulrich pointed out various aspects of the migration problem. He 

 stated that species may pass around rather than across basins, and that forms 

 do not always choose the shortest way across. 



After noting the pro])ortions of ammonites, pelecypods, brachiopods, and 

 other invertebrates in the Triassic faunas. Professor Schuchert remarked 

 that with the exception of the ammonites the types are all shallow-water 

 forms. Ammonites were powerful swimmers and probably did not float. Dur- 

 ing the development of geosynclines the ammonites lived in relatively shallow 

 waters. 



I'rof. J. C. Jones pointed out that in discussing the migration of these forms 

 it is necessary to consider also the course of oceanic currents. 



In answer to Professor Merriam's query whether the number of interre- 

 gional zones denoted a great length of time. Professor Smith replied that it 

 certainly implied a number of physiographic changes in the Triassic. He 

 stated further that he did not believe that climatic changes exerted a great 

 influence on the general evolution of these forms. 



