x LIST OF ILLUSTRATIONS 



FIGURES PAGE 



21. Ptyctodus ferox Eastman. Older and much worn lower dental plate 



from which the descending process has been broken away 136 



22. Ptyctodus ferox Eastman. Hamilton; Milwaukee, Wisconsin. Left 



upper dental plate showing facet due to wear against the lower 

 dentition 136 



23. Mylostoma variabile Newb. Cleveland shale; Sheffield, Ohio. Com- 



plete tritoral dentition arranged in natural position 162 



24. Macropetalichthys rapheidolabis Norw. & Owen. Middle Devonian; 



Indiana, Ohio and New York. Restoration of headshield show- 

 ing arrangement of cranial plates and course of sensory 

 canals 172 



25. Mylostoma variabile Newb. Cleveland shale; Cleveland, Ohio. Re^ 



toration showing two pairs of palato-pterygoid dental plates 

 arranged in their inferred normal position, and outlines of 



mandibular plates functioning against them 181 



2 p Coccosteus decipiens Agassiz. Lower Old Red Sandstone; Scotland. 



Lateral aspect restored by "Woodward, in part after Traquair. . 186 



27. Dinichthys halmodeus (Clarke). Marcellus shale; New York. Res- 



toration of headshield and dorsal armoring of trunk 192 



28. Dinichthys pustulosus Eastman. Middle Devonian; Iowa. Restora- 



tion of head-shield, dorsal aspect, showing arrangement of 

 cranial plates and course of sensory canals 197 



29. Neoceratodus forsteri (Krefft). Dorsal aspect of cranial roof, drawn 



as if flattened out to same extent as in Dinichthys 197 



30. Protitanichthys fossatus Eastm. Delaware limestone; Delaware, 



Ohio. Restoration of headshield showing transversely elong- 

 ated pineal and rostral plates, and sinuous suture-line between 

 the centrals 203 



31. Titanichthys agastizi Newberry. Restoration of headshield and dor- 



sal armoring of trunk 204 



^2. Dorso-median plate of a small unknown Arthrodire surviving as 

 late as the dawn of the Carboniferous. From nodule layer at 

 base of the Waverly in Boyle county, Kentucky 206 



33. Dipterus valencienncsi Sedgw. & Murch. Lower Old Red Sandstone: 



Scotland. Left lateral aspect as reported by Traquair 210 



34. Dipterus valencienncsi Sedgw. & Murch. Lower Old Red Sandstone; 



Orkney. Well preserved headshield showing cranial roofing 

 plates and sensory canals 234 



35. Scaumenacia curta (Whiteaves). Upper Devonian; Scaumenac Bay. 



Province of Quebec. Restoration of headshield based upon a 

 nearly complete individual 236 



36. Goelacanthus ivclleri Eastman. Kinderhook limestone; near Bur- 



lington, Iowa. Lateral aspect of holotype 249 



37. Pal (f ophichthys parvulus, sp. nov. Coal Measures; Mazon creek. 



Illinois. Lateral aspect of holotype showing elongate form of 

 body, degenerate squamation and continuous median fins 253 



38. Rhadinichthys devonicus (Clarke). Naples shale; Sparta, New York. 



Holotype 259 



