PLATE 37. 



Michelinia favositoidea. Devonian. 



Upper surface of a corallum from the blue clay of the Middle Devonian 

 Falls of the Ohio. Collection of the author. 



[Note. — With a lens of low power observe the papillose surface of the tabula and of the walls, the 

 latter dotting the longitudinal ridges. The author recommends the use of a double-convex lens, with 

 a power of about two diameters, in examining all the illustrations of this work. Viewed with such 

 a lens, all characteristic structural details will appear as they seem in the fossil itself, and "an atmos- 

 phere" so invests the figure that it may be studied almost as advantageously as the natural object.] 



