JAMES PERRIN SMITH 



29 



Lecanites, PI. Ill, figs. 1-3, an unprogressive or persistent form, an Am- 

 monite retarded in the Goniatite stage of development, probably 

 representing the radicle of the Ceratitoidea, and connecting them 

 with the Gephyroceratidse. 



Nannites, PI. Ill, figs. 4-8, a persistent, unprogressive type, a Mesozoic 

 Ammonite retarded in the Paleozoic Geniatite stage of development ; 

 probably representing the radicle of the Ptychitidae. 



Tropites, PL IV, figs. 11-21, a progressive Ammonite, showing distinct re- 

 capitulation, but with very unequal acceleration, or "telescoping*' of 

 characters and stages of development. 



Lytoceras, PI. XIV, fig. 10, a persistent group of Ammonites, lasting with 

 little change throughout the Mesozoic. 



Longobardites, PI. IX, figs. 14-16, family Pin- 1 



acoceratidae. 

 Eutomoceras, PL IX, figs. 5-7, family Hungar- 



itidae. 

 Discotropites, PL V, figs. 1-13, family Trop-| 



itidae. 

 Paratropites, PL V, figs. 14-19, family Trop- 



itidae. 

 Ceratites, PL V, figs. 20-26, family Ceratitidae. 



Gymnotropites, PL VIII, figs. 11-13, family 

 Tropitidae. 



Paraganides, PL VI, figs. 22-26, family Ptychitidae, retarded and rever- 

 sionary to the primitive Glyphioceran stock. 



Illustrating converg- 

 ence in different stocks, 

 in the development of 

 the keel and sculpture. 

 A good example of or- 

 thogenetie evolution. 



Leconteia, PL VI, figs. 11-15, family Trop- 

 itidae. 



Metasibirites, PL VI, figs. 1-10, family Trop- 

 itidae. 



Homerites, PL VI, figs. 16-21, family Trop- 

 itidae. 



Arpadites, PL VIII, figs. 1-10. \ 



Beyrichites, PL VIII, figs. 14-23. ' 



Reversionary, by ar- 

 jrest of development; 

 (showing vestigial char- 

 ^aeters, and probable or- 

 , thogenesis in closely al- 

 llied stocks. 



Showing reversion to 

 the ancestral Meekoce- 

 ras, in some characters. 



