JAMES PEKBIN SMITH 27 



ILLUSTRATIONS. 



Diagram, showing ideal recapitulation, with corresponding stages of 

 growth of the same size. Text-figure No. 1. 



Diagram, showing corresponding stages of growth in later forms reduced 

 in size. Text-figure No. 2. 



Diagram, showing theoretical recapitulation of phylogeny in ontogeny. 

 Text-figure No. 3. 



Diagram, showing actual recapitulation of phylogeny in ontogeny, with 

 lest stages. Text-figure No. 4. 



Diagram, showing genetic series, I showing theoretical straight natural 

 selection ; II showing periodic branching out from radicles ; III 

 showing orthogenetic series as seen in the paleontologic record. 

 Text-figure No. 5. 



Diagram showing the family tree of the Paleozoic and early Mesozoic 

 Ammonoid genera, showing the complex branching, and parallel 

 development of groups that are usually classed together. Text- 

 figure No. 6. 



Orthoceras, PI. XIV, fig. 1, a representative of the ancestral radicle of 

 the Cephalopoda. 



Cyrtoceras, PI. XIV, figs. 2 and 3, a transitional group, intermediate 

 between Orthoceras and Nautilus. 



Gyroceras, PI. XIV, fig. 4, a further development towards Nautilus. 

 Nautilus (Discites), PI. XIV, fig. 5, a close-coiled Paleozoic member of the 

 nautiloid group. 



Bactrites, PI. XIV, fig. 7, the primitive ancestral stock of the Ammo- 

 noidea, transitional from the orthoceran group. 



Mimoceras, PI. XIV, fig. 8, a primitive Goniatite, the probable ancestral 

 type of most of the Goniatitidae, transitional from Bactrites. 



Gephyroceras, PL III, figs. 9-11, the goniatite ancestor of the Ceratitoidea. 



Aganides, PL I, figs. 15 and 16, a primitive member of the Glyphio- 

 ceratidae, possibly transitional from Gephyroceratidae. 



