23 
24 
25 
26 
27 
28 
29 
30 
3 J 
32 
33 
34 
35 
36 
37 
38 
39 
40 
41 
42 
43 
44 
45 
46 
TABLE OF CONTENTS. 15 
Calymene senaria Green. Slice showing the large alimentary canal 79 
Ceraurus pleurexanthemus Green. Restoration of a longitundinal section 81 
Cryptolithus tessellatus Green. Cheek showing the genal oeca 84 
IUccnus. Volborth's figure of the heart 85 
Heart of Apus 85 
Isotelus gigas Dekay. The Panderian organs 91 
Ceraurus pleurexanthemus Green. Restoration, showing heart, alimentary canal, 
and extensor muscles .' 93 
The same. Longitudinal section of cephalon 95 
Niletis armadillo Dalman. Moberg's figure of the muscle-scars 95 
Marrella splendens Walcott. Restoration of the ventral surface 116 
Triarthrus becki Green. Appendage of the anterior part of the thorax 126 
Apus. Appendage from the anterior part of the trunk 127 
Weymouthia nobilis (Ford) 138 
Naraoia compacta Walcott 145 
Pagetia clytia Walcott 145 
Asaphiscus wheeleri Meek 145 
Padeumias robsonensis Burling 145 
Robcrgia sp 145 
Diagram showing possible lines of descent of the Arthropoda 150 
Triarthrus becki Green. Thoracic appendages '. 155 
The same. Pygidial appendages 157 
The same. Pygidial appendages 158 
Cryptolithus tessellatus Green. Drawing of the best single specimen 159 
The same. Part of the thorax and pygidium, with appendages 162 
Frontispiece. Charles Emerson Beecher, 1896. 
Plates 1-5. Photographs of Triarthrus becki, made by C. E. Beecher. 
Plate 6. Photographs of Triarthrus becki (figs. 1-3), Acidaspis trentonensis (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) 
i. Photographs of Cryptolithus tessellatus, made by C. E. Beecher. 
Drawings of Cryptolithus tessellatus, made by C. E. Beecher or under his 
direction. 
Photographs of Isotelus latus and /. inaxinius, made by C. E. Beecher. 
Drawing of a restoration of Ceraurus pleurexanthemus, made by Elvira 
Wood. 
Plates 
7- 
Plate 
9- 
Plate 
10. 
Plate 
11. 
