PHYLOGENY OF THE AETHEOPODA WITH M 

 PECIAL REFERENCE TO THE TRILOBITES 1 



PERCY E. RAYMOND, Ph.D. 

 Harvard University 



The phytogeny of the Arthropoda has been discussed 

 so often that merely to summarize previous opinions 

 would require an article of considerable length. In a re- 

 cent number of the Naturalist, 2 Professor Crampton has 

 reviewed the subject from the standpoint of a student of 

 insects, the most specialized Arthropoda. It may be of 

 interest to see what results are reached when approached 

 from the point of view of a student of the trilobites, the 

 most ancient members of the phylum. The characteris- 

 tics of trilobites may be summarized as follows : 



Appendages 



During the last two years I have had occasion to re- 

 study practically all of the known specimens of trilobites 

 whose appendages are preserved. The limbs of twelve 

 species, representing nine genera, are now more or less 

 fully known. Those which leave least to be desired are 

 Neolenus from the Middle Cambrian, Triarthrus, Caly- 

 mene, Ceraurus, and Cryptolithus from the Middle Ordo- 

 vician, and Isotelus from the Upper Ordovician. Repre- 

 sentatives of all three of the orders into which the class 

 is divided are included in this list, which contains exam- 

 ples of both ' 1 primitive" and ' 'specialized" trilobites. 



The appendages of all these genera, with the exception 

 of Isotelus, whose exopodites are still unknown, prove to 

 be constructed on one plan. An articulatory segment 



the trilobites now being published by the Connecticut Academy of Arts and 

 2 American Naturalist, Vol. 52, 1919, p. 143. 



398 



