The Ventral Armor of Dinichthys. — Wright. 313 
do not occur more abundantly where the white limestone is 
cut by the eruptives than they do elsewhere. The more prob- 
able explanation of their presence and abundance lies in the 
general metamorphism which the region has suffered, result- 
ing in the complete crystallization of the limestone and in the 
production of the abundant accessory minerals from the im- 
purities which it contained. 
THE VENTRAL ARMOR OF DINICHTHYS. 
By Albert A. Wright. Oberlin. Ohio. 
(Plate IX.) 
The reconstruction of the great placoderm Dinichthys still 
lacks much of completion. Although many important points 
have been made out, through the enthusiastic labors of the 
collectors, Hertzer, Gould, Kepler, Terrell, and Clark, and the 
descriptions of Newberry and Claypole, all of which consti- 
tute one of the most interesting and important chapters in 
American paleontology, it is still true that much yet remains 
to be done, owing to the scattered and often fragmentary 
condition of the material upon which reconstruction depends. 
Every year that field work is continued brings to light some 
new evidence as to the relative position of the plates and skel- 
etal elements of this fish. 
It is owing to the existence, in the museum of Oberlin col- 
lege, of some new and more perfect material than was in the 
hands of Dr. Newberry, that I am enabled to present a recon- 
struction of the armor that defended the ventral surface of 
Dinichthys. A description of this material was prepared in 
April, 1893, for the (now) forthcoming volume of the Ohio 
Geological Survey; and it is through the courtesy of the di- 
rector, Dr. Edward Orton, that I am enabled tit present the 
plate and cuts which accompanied that description here, in 
connection with this briefer summary of the facts. 
The only accounts of the ventral armor of Dinichthys which 
have hitherto heen published are those by Dr. Newberry in the 
report of the Ohio Survey* and in his monograph upon the 
*Ohio Geol. Survey, Paleontology, vol. n. 
