CONTENTS. 
Pag. 
I. Introduction .1 
II. Hiatorical.4 
III. Descriptive . 6 
The General Shape of the Cephalic Shield.6 
The Margins of the Oral Régions . 6 
The Serrations of the Anterior Margin of the Ventral Shield.7 
The Oral Plates. 8 
The Median Oral Plate.10 
The Median and the Lateral Eyes and the Olfactory Organ.14 
The Inner Surface of the Shield.18 
The Entapophyses.18 
The Lateral Line Organs.20 
IV. Summary and Conclusion .23 
A. Lateral Line Organs.23 
B. Sensory Openings of the Dorsal Shield ..28 
G. Lateral Eyes.23 
D. Posterior Marginal Openings.23 
E. The Median Eyes.24 
F. The Post-orbital Openings, or Olfactory Organs.24 
G. The Oral Plates.25 
H. The Anterior Margin of the Dorsal Shield.25 
I. The Appendages.25 
J. The Entapophyses.26 
K. The Resemblance betweenn the Tremataspidae and the Arthropods.26 
L. The Peltocephalata .28 
M. The Syncephalata .30 
List of Works cited. 
