73 
Explanation op Plate IV. 
Fig, 1. Pseudosphcsrexochus apollo, (Billings), Cranidium and thorax. Natural size. 
“ 2. The same species. Pygidium of a larger individual. Natural size, 
** 3. Brachyaspis altilis, Raymond, The type, from the dorsal side. J smaller 
than natural size. 
“ 4. Hcmigyraspis mcconnelli, Raymond. The type, which is distorted. The fig- 
ure is about i smaller than natural size. 
“ 5. Isotdoides homalonotoides, (Walcott). A specimen collected by Mr, W. A. 
Johnston at Kirkfield, Ont., and showing especially well the nasute ter- 
mination of the pygidium. Natural size. 
“ 6. Brachyaspis alacer, (Billings). Front view of the type for comparison with 
B. altilis. Notice the low eyes and the fiat glabella. 
“ 7. Brachyaspis altilis , Raymond. Front view, to show the course of thefacial 
suture, and the prominent eyes. About i less than natural size. 
“ 8. Isoteim maximus, Locke. A young specimen, to show the long spine at the 
genal angle. Slightly larger than natural size. 
