750 THE AMERICAN NATURALIST.  [Vow. XXXII. 
son with other diagrams. It is intended at some future time 
to reproduce a large scale photograph of the Rock Island 
cranium, on which most of the sutures and sensory canals are 
visible, in order to show the appearance in perspective of a 
form so highly arched from side to side as this. The most 
noteworthy feature regarding the sutures in this species is 
their prevailing undulatory outlines. No other Dinichthyid 
has them so sinuous, and even those of Coccosteus are less 
so in some regions. Beginning with the median occipital 
element (MO), we observe that it is longer and less tapering 
than in other species of Dinichthys, and is of about the same . 
relative proportions as in Coccosteus. But instead of being 
slightly sulcated anteriorly, as in C. canadensis and some other 
species, it is deeply lobed, and the anterior boundary is 
decidedly wavy. Immediately in front of the median and 
external occipitals lie the paired central elements (C), which 
exhibit almost identical relations with those of Coccosteus. 
Their anterior and lateral margins are more wavy than in 
Coccosteus, but their common longitudinal suture is less so. 
In advance of the centrals are the large preorbital plates 
(PrO), which are separated in front by presumably two median 
elements, the pineal (P) and rostral (R). It was impossible, 
however, to determine the relations of these two plates from 
any of the specimens that came under the writer’s observation, 
beyond that the pineal seems to be very narrow and without 
visible perforation. Likewise the boundary between pre- and 
postorbital plates is indistinct throughout the greater portion 
of its length; but it is believed that all of the remaining 
sutures are accurately delineated in the figure. 
One of the most marked points of similarity between D. 
pustulosus and Coccosteus is the fact that the central elements 
(C) are in contact with one another mesially throughout their 
entire length. These plates are similarly united in Phlycte- 
naspis, Brachydirus, Homosteus, and Titanichthys, which are 
sufficient to establish it as a general rule throughout the family 
Coccosteidæ. But an exception would appear to be furnished 
by D. intermedius and D. terrelli, provided we can depend 
upon the descriptions of earlier writers as trustworthy. The 
