LIST OF ILLUSTRATIONS ix 



FIGURES PAGE 



1. Thelodus scoticus Traq. Diagrammatic restoration showing dorsal 



fin and position of the eyes. Silurian of Scotland. 55 



2. Lanarkia spinosa Traq. Diagrammatic restoration similar to that 



of figure 1. Silurian of Scotland 55 



3. Ateleaspis tesselata Traq. Diagrammatic restored outline showing 



tail in profile. Silurian of Scotland 56 



4. Cephalaspis murchisoni Egert. Headshield seen from above, tail 



twisted to show dorsal fin and heterocercal tail mainly in side- 

 view. Old Red Sandstone, Great Britain 58 



5. Outlines of Acanthodian Fishes, illustrating their gradual elonga- 



tion in shape and loss of intermediate spines during succes- 

 sive periods. A, Climatius scutiger Egert. Lower Old Red. 

 Sandstone; Scotland. B, Mesacanthus mitchelli (Egert.) ; ibid. 



C, Acanthodes sulcatus Ag. Lo;ver Carboniferous; Edinburgh. 



D, Acanthodes gracilis Roemer. Lower Permian; Bohemia 60 



6. Cladoselache fyleri Newberry. Right side-view of a primitive shark 



illustrating the simplest kind of paddle-fins, which are sup- 

 ported by nearly parallel bars of internal cartilage. Upper 

 Devonian ; Ohio 61 



7. Pteraspis rostra'a Agassiz. Left lateral aspect of partially restored 



individual. Lower Old Red Sandstone, Great Britain 73 



8. Pterichthys testudinaris Agassiz. Left lateral aspect. Lower Old 



Red Sandstone ; Scotland 75 



9. Pterichthys millcri Agassiz. Restored outline of dorsal aspect. 



Lower Old Red Sandstone; Scotland 77 



10. The same from the ventral aspect 77 



11 Pterichthys milleri Agassiz. Restored outline of lateral aspect 77 



12. Bothriolepis canadensis Whiteaves. Restoration of dorsal aspect. 



Upper Devonian; Scaumenac Bay, Province of Quebec 88 



13. The same from the ventral aspect 88 



14. Bothriolepis canadensis Whiteaves. Lateral aspect of armor and 



body axis with two dorsal fins as restored by Dr. W. Patten. . 90 



15. Bothriolepis minor Newb. Antero-dorso-median with denuded su- 



perficial ornament. Catskill; Delaware county, New York 93 



16 Pleuracanthus decheni (Goldf.). Lower Permian; Bohemia. A 

 primitive shark showing elongated dorsal; diphy cereal caudal; 

 two anal; and paired fins with segmented basal cartilages and 

 actinotrichia. The branchial arches are believed to be seven in 

 number 102 



17. Gy 'r acanthus primaevus, sp. nov. Stafford limestone; New York.... 115 



18. Rhynchodus excavatus Newberry. Cedar Valley limestone; Waverly, 



Iowa. The dental plate here shown is the holotype of New- 

 berry's so-called R. occidentalis 125 



19. Rhynchodus pertenuis Eastman. Chemung; Delaware county, N. Y. 



Lower dental plate of holotype 132 



20. Ptyctodus ferox Eastman. Hamilton; Milwaukee, Wisconsin. Im- 



mature lower dental plate with well preserved descending proc- 

 ess at the front margin 136 



