PLATE 



Fig. 1. Triarthrus canadensis, free cheek from Craigleith, Ont., X 2. 



Fig. 2. Triarthrus canadensis, specimen from Rouge river, X 2. 



Fig. 3. Triarthrus canadensis, free cheek from Rouge river, X 2. 



Fig. 4. Triarthrus canadensis, cranidium from Rouge river, X 2. 



Fig. 5. Triarthrus glaber, BiUings' type of head, natural size. 



Fig. 6. Triarthrus glaber, variety with spine, Whitby, Ont., natural size. 



Fig. 7. Triarthrus spinosus rougensis, cranidium from Rouge river, X 2. 



Fig. 8. Triarthrus spinosus rougensis, type specimen. Rouge river, X 2. 



Fig. 9. Triarthrus spinosus, typical cranidium from Ottawa, X 2. 



Fig. 10. Triarthrus canadensis, pygidium from Rouge river, X 2. 



Fig. 11. Triarthrus spinosus rougensis, pygidium from Rouge river, X 2. 



