752 THE AMERICAN NATURALIST. (VoL XXXII. 
restorations of the cranial shield in these species, as given by 
Newberry, Claypole, and Dean, all show a subdivision of the 
space corresponding to the centrals in Coccosteus into two 
paired plates, which are designated as “ parietals”’ and “ fron- 
tals.” Claypole,! in describing the skull of D. intermedius, 
speaks as follows regarding the frontal plates: “ This area is 
well outlined in Dr. Newberry’s figures, where its boundaries 
are much more clearly marked than in the specimen now 
described.” And again, in regard to the “ parietals” he says: 
“Judging from the conventional form which he has given to 
this plate in his restoration, its outlines cannot have been 
clearly defined in the specimen which Dr. Newberry studied. 
Instead of the small and elliptical area which he has assigned 
to it, it has a large size and an irregular outline.” We see 
from this that Newberry’s specimen (or specimens) failed to 
show perfectly the boundaries of one of the subdivisions of 
the central plate, and Claypole’s failed to show the other. It 
is fair to allow that appearances may have been suggestive of 
a division in some examples ; but the writer can only state 
from his personal experience that he has not yet been able to 
observe such a division of the centrals in D. intermedius and 
D. terrelli, and is positive that none exists in D. pustulosus. 
We will revert to this matter again under the head of the first- 
named species. 
The arrangement of sensory canals in D. pustulosus is very 
much the same as in other species of this genus, except that 
they are more curved, especially the preorbital canal, thus 
recalling the conditions in Coccosteus. In the latter genus, 
but not in Dinichthys, a lyra is formed in the middle of the 
shield by the disposition of sensory canals on the central ele- 
ments. That is to say, the canals following the boundary of 
the median occipital bend around towards each other, and a 
transverse channel connects the point of origin of the pre- 
and postorbital canal systems. A survival of this lyrate 
arrangement exists in D. pustulosus, in that occasionally one 
or more short, slightly curved, independent canals are seen to 
1 Claypole, E. W. The Head of Dinichthys, Amer. Geol., vol. x (1892), PP- 
199-207. 
