164 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 57 



mediate between Aglaspina and the Eurypterida, and that the two 

 orders Limulava and Aglaspina serve to connect the Trilobita and 

 the Eurypterida. 



From the Eurypterida we pass to the Xiphosura. It is thought 

 that the Phyllocarida, as represented by the group of forms included 

 under the Hymenocarina, came from the Branchiopoda, but on a 

 different line of descent from the Trilobita and the orders grouped 

 under the Merostomata. 



The ostracods are assumed to have been derived from the Branchi- 

 opoda but on a different line of descent from the Trilobita and Phyllo- 

 carida. 



Phyllocarida 



Ostracoda 



Eurypterida 



Aglaspina 



Branchiopoda 

 ■■ Apodidae 



Theoretical Evolution of Cambrian Crustacea from the Branchiopoda 



I will not attempt further to discuss the various lines of descent 

 of the genera in this preliminary notice, as in the spring of 19 13 

 much more material may be available for study. The outline 

 diagram (p. 161) indicates my present view, though this is tentative 

 pending study and comparison with living forms. Any speculation 

 on the origin of the various invertebrate groups based on the faunas 

 found in the Cambrian must necessarily be very defective, as the pre- 

 Cambrian development extended far back into pre-Cambrian time. 



RELATION TO RECENT CRUSTACEANS 

 That the Burgess shale crustacean fauna was a tremendous sur- 

 prise to me and that it will be to all paleozoologists is evident to 

 any one acquainted with what was known of the early Paleozoic 



