PLATE V1I1 A— Continued. 



Phacops Logani, Hall. 



Fig. 19. The type S] Lmen, figured in Palaeontology of New York, vol. iii, pi. 73, tig-. IT). 



[ntroduced for comparison with the Upper Helderberg species of Phacops. 

 Fig. Jo. A cephalon of this species, enlarged one diameter, retaining normal proportions and showing the 

 glabellar furrows and genal spines. 



Lower Helderberg group. Schoharie, Schoharie county. 



Phacops i;a\a. 



See Plates 6, 7, 8 and 25. 

 A small individual, showing normal proportions ami a perfect dorsal surface. 



Hamilton group. Eighteen-mile Creek, Erie county. 

 A larger ami unusually perfect, individual, showing the glabellar furrows on the dorsal surface. 



Hamilton group. Darieii, Genesee county. 

 An individual retaining the crust in perfection, but not normally extended. 

 Profile of the same. 



Hamilton group. In tin- drift at Ann Arbor, Michigan. 

 Fig. 2n. An individual, compressed laterally, parallel to the cleavage'planes of the shales, a frequent mode 



of preservation. 

 Fig. 26. Anterior view of the same. 



Hamilton group. Eighteen-mile Creek, Erie county. 

 Pig. 27. A very small enrolled individual. 



Hamilton group. Eighteen-mile Creek, Erie county. 

 Fig. 28. A still smaller, enrolled example. 



Hamilton group. Canandaigua Lol,t . 

 Fig. 2'.i. The hypostoma of a large individual, retaining only a small portion of the crust. 



Hamilton group. Canandaigua Lake. 

 Fig. 30. An internal east of the cephalic doublure and a portion of the thorax, enlarged one diameter to 

 show the crenulations of the sub-frontal sulcus. 



Hamilton group. Fultonham, Schoharie county. 

 Fig. 31. A portion of the thorax, enlarged one diameter j snowing the internal surface of the axial arches 

 and their prolongation into the \ isceral supports or processes for the attachment of the ambu- 

 latory 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 ventral axial processes through the translucent calcite with which the interior 

 space is filled. The specimen also shows a section of the hypostoma. indicating the'deep and 

 abrupt deflection on it.- posterior margin. The drawing gives an enlargement to two diameters. 

 Hamilton group. Canandaigua. Ontario county. 

 Fig. :'.:'.. 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 

 margin may represent the ventral membrane beneath the viscera. 

 Hamilton group. Canandaigua, Ontario county. 



Bronteus Tullii is. 



Page 12. 

 Fig. 34. The pygidium, natural size. 

 Fig. 35. The same, enlarged to two diameters. 



Tully limestone. Kingsley's Hill, near Otisco, Onondaga comity. 

 Pig. 36. The frontal doublure, probably belonging to the same species. 



Tully limestone. Uoroiliim, Onondaga county. 



