ERRATA. 
The color plates are the work of the Bureau of Engraving, Inc., Minne- 
apolis, Minn. For some reason their mark was omitted from the face of 
the plates. 
Color plate II was not reduced as ordered, therefore the magnifica- 
tions are incorrect. 
Fig. 1. Magnification 4.5 instead of 3.50 
Fig. 2. Magnification 5.0 instead of 3.90 
Fig. 3. Magnification .9 instead of .70 
Fig. 4. Magnification 4.5 instead of 3.50 
Fig. 5. Magnification .9 instead of .70 
Fig. 6. Magnification .9 instead of .70 
Fig. 7. Magnification 2.1 instead of 1.66 
Fig. 8. Magnification 2.8 instead of 2.20 
Fig. 9. Magnification 1.8 instead of 1.40 
(328) 
