PLATE VII, 



Fig. 20. Inferior aspect of the mandible of ^mia calva, showing the normal position 

 of the galar plate, G. pi. Life size from nature, by the author. 



Fig. 21. A longitudinal, vertical, median section of the cranium of a perch {Perm 



americana), mside view showing the relations of the various bones, the 



position of the otolith, the eye-muscle canal, and the bones that enter into 



• the ear capsule. Adult. Slightly enlarged from nature, by the author, 



from his own dissections. 



108 



854 



