A Shew Genus of Silurian Fishes. 
71 
armoured above and below, it will be the type of a new genus 
for which the name Diplaspis will be appropriate.* 
In Pteraspis (Kner), which, however, is a Devonian and 
not a Silurian genus, there is a considerable resemblance in 
the ornamentation of the shield, and generally in the dorsal 
armature, to the covering plates of the Acadian fish; but if 
we attempt to compare the different plates of which the shield 
of our Pteraspidian fish is composed with those of Pteraspis, 
they will be found to differ widely from that genus. On the 
other hand, if the plates a, b, b ; and c, be compared with those 
of the genus Cyathaspis (Lankester) the correspondence of 
parts is striking. 
In Prof. E. Ray Lankester’s monograph on the fishes of the 
Old Red Sandstone f we appear to have only one example of 
this genus ( Cycithaspis ) described, for although Cycithaspis (?) 
Symonclsi is described under this head, it seems very doubtful 
whether it should be so referred; and Prof. Lankester appears 
to have placed it here provisionally only. The typical species, 
C. BanTcsii (Huxley and Salter), is Silurian, and possesses a 
set of plates quite analagous to the dorsal covering of the 
Acadian fish. There is also on the central plate (“ dorsal 
scute ”) a tubercle, indicated in Prof. Lankester’s figures, 
which holds the place of a similar circular elevation on the 
shield of the Acadian fossil (see plate c.) In Prof. Lankester’s 
examples of C. BanTcsii , the surface markings appear to have 
been obscure, except on the rostral and lateral plates; we do 
not know, therefore, how far the markings on the main plate 
of each of these two fishes were similar. 
Curiously enough, the plate d possesses characteristics 
analagous to those of the scute of the genus Scaphaspis (Lank, 
ester). The markings on the surface of this plate are almost 
exactly parallel to those of the “ dorsal ” scute of Scaphaspis 
truncata (Huxley and Salter), in the fine example figured by 
Prof. Lankester (plate II., fig. 3, Memoirs cited), and the plate 
is similarly a little asymmetrical. 
* The specific name has already been given, as it has been described in the 
“ Canadian Record of Science ” under the name of Pteraspis (?) Acadica. 1886,, 
pp. 251 and 252 and 323-5. 
t Memoirs of the Palseontographical Society, London. Vol. XXI. 
