Chapter IV: 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 appendages to marking on
dorsal surface of glabella 43
Anal plate 44

The appendages of _Ptychoparia_ 45
_Ptychoparia striata_ (Emmrich) 45
_Ptychoparia cordilleræ_ (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 branchiæ 48
Ventral membrane 50
Appendifers 51

_Calymene senaria_ Conrad 52
Cephalic appendages 52
Thoracic appendages 53
Pygidial appendages 54
Relation of hypostoma to cephalon in _Calymene_ 55
Restoration of _Calymene_ 56

_Calymene_ sp. ind. 56

_Ceraurus pleurexanthemus_ Green 57
Cephalic appendages 58
Thoracic appendages 59
Pygidial appendages 59
Relation of hypostoma to cephalon 59
Restoration of _Ceraurus pleurexanthemus_ 60
The appendages of _Acidaspis trentonensis_ Walcott 61

The appendages of _Cryptolithus_ (see also Part IV) 61
_Cryptolithus tessellatus_ Green 61
Restoration of _Cryptolithus_ 62

Summary on the ventral anatomy of trilobites 64
Comparison of appendages of different genera 64
Coxopodite 64
Cephalon 64
Thorax 66
Pygidium 67
Caudal rami 68
Homology of cephalic appendages with those of
other Crustacea 69
Functions of the appendages 70
Antennules 70
Exopodites 70
Endopodites 71
Use of the pygidium in swimming 72
Coxopodites 74
Position of the appendages in life 74