22 ACCELERATION OP DEVELOPMENT IN FOSSIL CEPHALOPODA 



(Episageceras), Lecanites (Paralecanites), Dalmatites, Popanoceras, 

 Celtites (Paraceltites). 



The following Permian genera had reached a stage of development 

 as high as that of Triassic forms, but are not yet known in Triassic 

 faunas: Cyclolohus, Waagenoceras, Thalassoceras, Stacheoceras. The 

 following genera appear at the very bottom of the Triassic, already 

 fully developed, and must have existed somewhere during Permian 

 time, although they are not yet known in any Permian faunas : Ussuria, 

 Columbites, MonophylUtes, Nannites, Meekoceras, Flemingites, Heden- 

 stroemia, Pseudosageceras, Ophiceras, Aspenites, Lanceolites, Cordiller- 

 ites. Kymatites and Amhites of Waagen may not be goniatitic survivors 

 from the Permian faunas, but merely Meekoceratidae in which the lobes 

 have not been well preserved on account of weathering. The later 

 groups, such as Proavites, Metasihirites, Paraganides, Tornquistites, 

 Dieneria, Leconteia, Tropiceltites, Styrites, Polycyclus and Lohites, all of 

 which are as simple as Permian forms, are merely cases of arrested de- 

 velopment and reversion. 



Karpinsky's* work in tracing the Ammonoids of the Carboniferous 

 into the Permian, and comparison of ontogeny with phylogeny, has given 

 us our most convincing example of real genetic series. The work of J. 

 P. Smith** has carried our knowledge of the Ammonites further back 

 into the Carboniferous, and later he has traced many of the Carbonifer- 

 ous genera and families into the Triassic,* combining the study of onto- 

 geny and phylogeny. 



The monographs of Diener, von Krafft, and Waagen, on the Lower 

 Triassic Cephalopoda of India, of Kittl and von Arthaber on those of 

 the Mediterranean Kegion, have added greatly to our knowledge of the 

 transitional faunas at the border-line between Paleozoic and Mesozoic, 

 and out of them have come some real genetic series. The combined re- 

 sult of all this work is given here in the form of a table showing the re- 

 lationship of the early Mesozoic Ammonoids to those of the Paleozoic. 



*Ueber die Ammoneen der Artinsk-Stufe, Mem. Acad. Imper. Sci. St. P^ters- 

 bourg, 7th Ser. Vol. XXXVII, No. 2, 1889. 



**The Carboniferous Ammonoids of America, Mon. XLII, U. S. Geological 

 Survey, 1903. 



*The Triassic Cephalopod Genera of America, Prof. Papers No. XL, U. S. 

 Geol. Survey, 1905. 



