PRELIMINARY NOTE. 
The preparation of the following memoir was begun by Mr. Garman 
during my term of service as Director of the Kentucky Geological Sur- 
vey. Circumstances have made it necessary to delay its publication to 
the present date. 
In the act of 1874, providing for the continuance of the Geological Sur- 
vey, the Legislature of Kentucky permits “that the scientific results of 
the Survey may be published in any scientific journal by permission of 
the Director.” Although this memoir will form a part of the second 
volume of Memoirs of the Kentucky Survey, it seems to me highly 
desirable that it should secure the wider circulation that will be given 
to it by this publication in the memoirs of the Museum of Comparative 
Zoology. The Kentucky Survey is fortunate in being able, by this 
arrangement, to acknowledge the large debt it owes to this Museum for 
“most effective aid in every step of its scientific work. 
N. 8. SHALER, 
Formerly Director of the Kentucky Geological Survey. 
CAMBRIDGE, Mass., June, 1883. 
