TABLE OF CONTENTS. 
Historical review 17 
Part I. The appendages of trilobites 20 
Terminology 20 
The appendages of Neolenus 21 
Historical 21 
Neolenus serratus (Rominger) 21 
Cephalon 21 
Thorax 22 
Pygidium .■ 23 
Epipodites and exites 23 
Description of individual specimens 23 
Restoration of Neolenus 30 
Nathorstia transitans Walcott 31 
The appendages of Isotelus 32 
Historical 32 
Isotelus latus Raymond 34 
Isotelus maximus Locke 35 
Restoration of Isotelus 37 
Isotelus gigas Dekay 37 
Isotelus arenicola Raymond 39 
The appendages of Triarthrus (see also Part IV) 39 
Triarthrus becki Green 39 
Historical ' 40 
Restoration of Triarthrus 42 
Relation of cephalic appendagess to marking on dorsal surface of glabella 43 
Anal plate 44 
The appendages of Ptychoparia 45 
Ptychoparia striata (Emmrich) 45 
Ptychoparia cordillcrcc (Rominger) 45 
Ptychoparia permulta Walcott 45 
The appendages of Kootenia 46 
Kootenia dawsoni Walcott 46 
The appendages of Calymene and Ceraurus 46 
Historical 46 
Comparison of the appendages of Calymene and Ceraurus with those of 
Triarthrus 47 
Spiral branchi?e 48 
Ventral membrane 5° 
Appendifers 5 1 
Calymene senaria Conrad 5 2 
Cephalic appendages 5 2 
Thoracic appendages 53 
Pygidial appendages 54 
