PLATE XVI 
Acidaspis callicera. 
Page 69. 
Fig. 1. An imperfect specimen, natural size, retaining the head and six thoracic segments. 
Fig. 2. The same, enlarged to two diameters. 
Corniferous limestone. Camilhis, Onondaga cormty. 
Fig. 3. A laj’ger, more nearly entii-e individual, drawn to two diameters. The specimen is an internal 
cast in decomposed chei-t, and has the cephalon somewhat deflected. 
Fig. 4. Profile of the same, similarly enlarged. 
Fig. 5. An anterior view of the same, showing the elevation of the glabella and eye-lobes. 
Fig. 6. The natural mould of the dorsal surface of the same sx^ecimen, similarly enlarged. 
Fig. 7. A gutta-xiercha imxiression from this mould, showing the ornamentation of the surface. 
Upper Heldei’berg limestone. Cayuga, Province of Ontario. 
Fig. 8. The glabellar x^ortion of a small cephalon, enlarged to two diameters. 
Uxiper Helderberg limestone. Cay uga, Province of Ontario. 
Fig. 9. The left movable cheek, showing the length of the marginal and genal sxunes. Enlarged to four 
diameters. 
Corniferous limestone. Canandaigua, Ontario cou7ity. 
Fig. 10. The glaliellar xiortion of a head, enlarged to two diameters, showing the denticulations on the 
frontal margin. 
Uxiper Helderberg limestone. Cayuga, Province of Ontario. 
Figs. 11 and 12. Right and left movable cheeks, drawn from internal casts, and showing the number of 
marginal spines. 
Upxier Helderberg limestone. Cayitga, Pi'ovince of Ontario. 
Fig. 13. Lateral view of a left movable cheek, retaining the eye. Enlarged to two diameters. 
Schoharie grit. Near Clarksville, Albany county. 
Acidaspis, sp. 
Page 71. 
Fig. 14. An imxierfect xiygidium, enlarged to two diametei'S. 
Uxiper Helderberg limestone. Cayuga, Province of O^itaiio. 
Acidaspis Romingeri. 
Page 71. 
A fragmentary pygidium, restored in outline to show the great length of the marginal spines. 
Enlarged to two diameters. 
The same in xirofile. 
A xiortion of the anterior marginal spine of the same sxiecimen, to show the character of the 
ornamentation. Enlarged to six diameters. 
A similar enlargement of the terminal portion of the fourth marginal sxiine. 
Hamilton group. Little Traverse Bay, Michigan. 
Fig. 15. 
Fig. 16. 
Fig. 17. 
Fig. 18. 
