PLATE VIII A— Continueil. 
Phacops Logaxi, Ililll. 
Fig-. 19. The type specimen, figured in Palaeontology of New York, vol. iii, pi. 73, fig. 15. 
Introduced for compai-ison with the Upper Helderberg species of Pliaco'ps. 
Fig. 20. A cephalon of this species, enlarged one diameter, retaining normal proportions and showing the 
glabellar furrows and genal spines. 
Lower Helderberg gj-oup. Schoharie, Schoharie county. 
Phacops rana. 
See Plates 6, 7, 8 and 25. 
Fig. 21. A small individual, showing noi-mal proiiortions and a perfect dorsal surface. 
Hamilton group. Eighteen-niile Creek, Erie county. 
Fig. 22. A larger and unusually pei-fect individual, showing the glabellar furrows on the dorsal sui-face. 
Hamilton groiqi. Darien, Genesee county. 
Fig. 23. An individual retaining the crust in perfection, but not normally extended. 
Fig. 24. Profile of the same. 
Hamilton group. In the drift at Ann Arbor, Michigan. 
Pig. 25. An individual, comiiressed laterally, parallel to the cleavage'planes of the shales, a frequent mode 
of jn-eservation. 
Fig. 26. Anterior view of the same. 
Hamilton group. Eighteen-mile Creek, Erie county. 
Fig. 27. A very small enrolled individual. 
Hamilton grouji. Eighteen-mile Creek, Erie comity. 
Fig. 28. A still smaller, enrolled example. 
Hamilton group. Canandaigua Lake. 
Fig. 29. The hypostoma of a lai-g-e individual, retaining only a small iwrtion of the crust. 
Hamilton group. Canandaigua Lake. 
Fig. 30. An internal cast of the cephalic doublure and a portion of the thorax, enlarged one diameter to 
show the ci-enulations of the sub-frontal sulcus. 
Hamilton gi-oup. Fultonham, Schoharie county. 
Fig. 31. A portion of the thorax, enlarged one diameter ; showing- the internal sui-face of the axial arches 
and their prolongation into the visceral supports or processes for the attachment of the ambu- 
latoi-y muscular apparatus. . , 
Hamilton group^ Canandaigua Lake. 
Fig. 32. A vertical section through an enrolled individual, cut near the axial furrow, and showing the 
projection of the venti-al axial processes through the translucent calcite with which the intei-ior 
space is filled. The specimen also shows a section of the hypostoma, indicating the deep and 
abrupt deflection on its posterior margin. The di-awing gives an enlargement to two diameters. 
Hamilton group. Canandaigua, Ontario county. 
Fig. . 33. A section of an enrolled example, cut along the middle line of the axis, retaining only the thoracic 
portion, and showing three of the ventral processes. The light line parallel with the upper 
mai-gin may represent the ventral membrane beneath the -viscei-a. 
Hamilton group. Canandaigua, Ontario coxinty. 
Brontkus Tullius. 
Rage 1-2. 
Fig. 34. The pygidium, natural size. 
Fig. 35. The same, enlarged to two diameters. 
Tully limestone. Kingsley's Hill, near Otisco, Onondaga county. 
Fig. 36. The frontal doublure, probably belonging to the same species'. 
Tully limestone. Borodino, Onondaga county. 
