2 go AN INTRODUCTION TO THE STUDY OF FOSSILS 



8. Describe the ventral protection of the animal. 



9. What ventral appendages were there ? 



10. Why are the ventral appendages so seldom found ? 



11. What were the principal muscles of the body? Where 

 located ? Their function ? 



12. What was the character of the food of Triarthrus ? How 

 procured ? 



13. Trace the food through the digestive canal and its diges- 

 tion. 



14. Give the probable character of the blood circulatory 

 system ; the nervous system. 



15. What sense organs did Triarthrus possess ? 



16. How did it breathe? 



17. By what means is the embryology of such a fossil form as 

 Triarthrus known ? 



18. What is the protaspis ? Its characters ? 



19. How did the trilobite increase in size from this early larval 

 condition to the adult ? 



20. What reasons are there for believing that trilobites were 

 bisexual ? 



21. What reasons for placing the trilobites in the class Crus- 

 tacea ? 



22. Why are trilobites made a separate sub-class, and that 

 the most primitive? 



General Survey of Sub-class Trilobita 



The trilobites are extinct marine crustaceans with the body 

 divided into a variable number of segments, and entirely incased 

 in a protective chitinous skeleton ; this is thickened and har- 

 dened with lime carbonate where no movement is required, but 

 thin and flexible in the intermediate spaces. These thin places 

 act as joints and it is here that after the molting or death of the 

 animal a rather easy separation of the skeletal elements takes 

 place. 



Trilobites were undoubtedly marine, since they are always 

 found associated with such forms as corals, crinoids, brachio- 

 pods and cephalopods, the living representatives of which are 

 wholly marine. They lived during the entire Paleozoic, from 

 the Cambrian to the Permian, inclusive. 



