ZOOLOGICAL POSITION OF THE TRILOBITES. 49 



From this brief account of the rise of the modern 

 Crustacea from Apus, it follows that the Trilobites are, in 

 reality, pre-crustacean. They represent a stage more 

 primitive than Apus, i.e., nearer to the original annelidan 

 ancestor of the whole phylum. 



While the immediate ancestors of Apus and of the 

 Crustacea proper retained the power of swimming freely 

 from place to place, the Trilobites became specialised for 

 a creeping manner of life, apparently perfecting along one 

 line the new method of feeding, which, as above described, 

 was the physiological change leading to the subsequent 

 morphological transformation of the Chaetopod into the 

 Crustacean. 



We may therefore describe the Trilobites as specialised 

 links in the chain which connects the Crustacea with their 

 annelidan ancestors. 



RECENT PAPERS ON THE TRILOBITES. 



C. E. Beecher. On the Thoracic Legs of Triarthrus. Am. 



Jour. Set., ser. 3, vol. xlvi., 1893. 

 C. E. Beecher. On the Mode of Occurrence and the Structure 



and Development of Triarthrus Beckii. Am. Geo/, vol. xiii., 



1894. 

 C. E. BEECHER. Appendages of the Pygidium of Triarthrus. 



Am. Jour. Sci., vol. xlvii., 1894. 

 C. E. Beecher. Further Observations on the Ventral Structure 



of Triarthrus. Am. Geo/., vol. xv., 1895. 

 C. E. Beecher. Structure and Appendages of Trinucleus. 



Am. Jour. Sci., xlix., 1895. 

 H. M. Bernard. The Apodidce. Macmillan's Nature Series, 1892. 

 H. M. Bernard. The Systematic Position of the Trilobites. 



Quart. Jour. Geo/. Soc., vol. 1., 1894, and vol. li., 1895. 

 W. D. MATTHEW. On Antennae and other Appendages of Triar- 

 thrus Beckii. Amer. Joiir. Sci., ser. 3, vol. xlvi., 1893. 

 C. D. Walcott. Fauna of the Olene/lus Zone. U.S. Geo. Surv. 



Tenth Report, 1890. 

 C. D. WALCOTT. Note on some Appendages of the Trilobites. 



Geo/. Mag., June, 1894. 



H. M. Bernard. 



