EVOLUTION OF FOSSIL CEPHALOPODA. 



249 



of Jurassic ammonites figured by Quenstedt.* Quite 

 recently Prof. W. Waagen f has called attention to the 

 likeness of certain Trachyostraca to Jurassic genera, 

 and indicated the probability of genetic relationships. 

 But Mojsisovics J says that these similarities have noth- 

 ing to do with relationship, but are purely " converg- 

 ence phenomena," whatever that may mean. Resem- 

 blance of adults of Triassic and Jurassic forms might 

 with some reason be ascribed to this mysterious agency, 

 but surely no biologist would thus explain away the re- 

 semblance of larval and adolescent stages of Jurassic 

 ammonites to adult Trachyostraca of the Trias. There 

 was some excuse for such opinions as long as the fauna 

 of the upper Trias was not well known, and there was 

 apparently a great break in the series of ammonites. But 

 after the appearance of the monographs of G. von Art- 

 haber, Diener, Mojsisovics, and Waagen,* on the Triassic 

 faunas of the Alps, Himalayas, the Salt Range of India, 

 and Siberia, there is no longer any such excuse. Ancestral 

 types, long predicted by larval stages of Jurassic ammo- 

 nites, may be seen in these works, as, for instance, Tropi- 

 cettites, which is exactly like the neanic stage of Amal- 

 theus ; but the great variety is confusing, and correla- 

 tion difficult, on account of unsatisfactory classification. 

 The only solution of the problem is to classify ge- 

 netically the Paleozoic goniatites, and from them work 

 upward into the Permian and Lower Triassic ammonites. 

 These older groups have simpler larval stages, are not 

 very greatly accelerated, and repeat clearly their an- 

 cestral history. When this is done the radicles will all 



* Ammoniten des Schwabischen Jura. 



f Pal. Indica, Salt Range Fossils, vol. ii, p. 122. 

 \ Das Gebirge um Hallstadt, Bd. ii, p. 265. 



* For literature on Triassic faunas, see Jour. Geol., vol. iv, No. 

 4, J. P. Smith, Classification of Marine Trias. 



