Plate XIII. 



Baculites chicoensis Trask, Upper Cretaceous, California. 



Pigs. 1-9, larval stages, showing coiled young, and derivation from 

 the normal genus, Lytoceras. 



Lytoceras alamedense Smith, Upper Cretaceous, California. 



Figs. 10-15. Larval and adolescent stages, showing resemblance to 

 young of Baculites. 



Schloenbachia oregonensis Anderson, Upper Cretaceous, Oregon. 

 Figs. 16-21, larval and adolescent stages. 



Placenticeras pacificutn Smith, Upper Cretaceous, California. 



Figs. 22-28. Larval and adolescent stages, showing recapitulation of 

 phylogeny in ontogeny. 



Lytoceras, Schloenbachia, and Placenticeras belong to wholly different 

 stocks, with different ancestry; and yet their young stages are very 

 much alike, due to adaptation and not atavism. 

 All figures are from J. P. Smith, figs. 1-9, Larval Coil of Baculites, 

 American Naturalist, 1901 ; figs. 10-15, The Development of Lytoceras 

 and Phylloceras, Proc. Calif. Acad. Sci., 1898; figs. 16-21, Larval Stages 

 of Schloenbachia, Journal of Morphology, 1899 ; figs. 22-28, The Develop- 

 ment and Phylogeny of Placenticeras, Proc. Calif. Acad. Sci., 1900. 



