316 The American Geologist. November, 1894 
more fully described as the suborbitals. The vacancy thus 
created in the ventral shield was not positively filled by any- 
thing described in the monograph. The subject is alluded to 
as follows: "No figure is given of the plates which are suit- 
posed to have formed the posterior half of the plastron, be- 
cause no perfect ones have been found; but I have numerous 
fragments of relatively large plates which must have been 
oblong in form and had the moderate and uniform thickness 
and plainness of surface which characterize the plates that 
defended the under side of the body. As they are apparently 
assignable to no other place in the armor of Dinichthys, I 
provisionally locate them here."* Specimens of each of the 
other bones, except the median, are figured in the mono- 
graph, that is to say, the anterior ventro-lateral of two spe- 
cies, a single hyoid? and a single jugular ; but these are all 
isolated and no diagram or figure is given which groups them 
in their relative positions in the armor as a whole. 
A careful study of the new and well preserved material in 
my hands convinces me that the ventral armor of Dinichthys 
must be reconstructed as follows : 
1st. The anterior ventrolaterals should remain in the posi- 
tion to which they were first assigned by Dr. Newberry. 
2d. The bone figured as "hyoid" with an interrogation 
mark in the monograph was probably assigned to its position 
on insufficient evidence, and its true relations are still prob- 
lematical. 
3d. The arched "jugulars" must be transferred to the pos- 
terior end of the ventral shield, where they constitute the 
posterior ventrolaterals, the arched border being directed 
backwards instead of forwards. They thus fill the vacancy 
caused by the removal of the suborbitals to the sides of the 
head. 
4th. The median plate or plates should doubtless retain 
their place as previously described by Dr. Newberry. I have 
seen no specimens of these, but the rearrangement proposed 
will scarcely atfect them. 
By these changes the "jugulars" and "hyoids" disappear, 
and the armor or other structures upon the under side of the 
head remain to be discovered. 
*Op. cit., p. 138. 
