JAMES PERRIN SMITH 



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FIG. 6. 



It is not complete, and is, of course, subject to constant revision, but it 

 does show probable genetic series, in the light of our present knowledge 

 of the subject. 



In his studies of the genealogy of Jurassic and Cretaceous genera 

 Steinmann* has gone to great lengths in finding genetic connections with 

 Triassic genera, where connecting links are absolutely unknown, and ex- 

 tremely improbable. In seme instances he does make a strong case for 

 relationship, but none for generic persistence. The doubtful relation- 



*Rassenpersistenz bei Ammoniteii. Eine Erwiderung. Centralblatt fiir 

 Geol. Min. und Pal. 1909, No. 8, pp. 199-203, and 225-232; and in Probleme der 

 Aramoniten-Phylogenie (Gattiing Heterotissotia), Niederrhein. Gesell. fiir Natur. 

 etc. 1909, pp. 1-16; also in Die Abstammung der "Gattung Oppelia" Waagen. 

 Centralblatt fiir Geol. etc. 1909, No. 21, pp. 641-646. 



