TABLE OF CONTENTS. 15 



23. Calymene senaria Green. Slice showing the large alimentary canal 79 



24. Ceraurus pleurexanthemus Green. Restoration of a longitundinal section 81 



25. Cryptolithus tessellatus Green. Cheek showing the genal caeca 84 



26. Illcenus. Volborth's figure of the heart 85 



27. Heart of Apus 85 



28. Isotelus gigas Dekay. The Panderian organs 91 



29. Ceraurus pleurexanthemus Green. Restoration, showing heart, alimentary canal, 



and extensor muscles 93 



30. The same. Longitudinal section of cephalon 95 



31. Nilcus armadillo Dalman. Moberg's figure of the muscle-scars 95 



32. Marrella splendens Walcott. Restoration of the ventral surface 116 



33. Triarthrus bccki Green. Appendage of the anterior part of the thorax 126 



34. Apus. Appendage from the anterior part of the trunk 127 



35. Weymouthia nobilis (Ford) 138 



36. Naraoia compacta Walcott 145 



37. Pagetia clytia Walcott 145 



38. Asaphiscus wheelcri Meek 145 



39. Pcedeumias robsonensis Burling 145 



40. Robcrgia sp 145 



41. Diagram showing possible lines of descent of the Arthropoda 150 



42. Triarthrus bccki Green. Thoracic appendages 155 



43. The same. Pygidial appendages 157 



44. The same. Pygidial appendages 158 



45. Cryptolithus tessellatus Green. Drawing of the best single specimen 159 



46. The same. Part of the thorax and pygidium, with appendages 162 



Frontispiece. Charles Emerson Beecher, 1896. 



Plates 1-5. Photographs of Triarthrus bccki, made by C. E. Beecher. 



Plate 6. Photographs of Triarthrus bccki (figs. 1-3), Acidaspis trcntonensis (fig. 

 6), and Cryptolithus tessellatus (fig. 7), made by C. E. Beecher. Photo- 

 graphs of the endopodites of a probable species of Calymene (figs. 4, 5) 



Plates 7-8. Photographs of Cryptolithus tessellatus, made by C. E. Beecher. 



Plate 9. Drawings of Cryptolithus tessellatus, made by C. E. Beecher or under his 

 direction. 



Plate 10. Photographs of Isotelus latus and /. maximus, made by C. E. Beecher. 



Plate n. Drawing of a restoration of Ceraurus pleurexanthemus, made by Elvira 

 Wood. 



