A Flew Genus of Silurian Fishes . 
69 
ARTICLE IV. 
A PRELIMINARY NOTICE OF A NEW GENUS OF 
SILURIAN FISHES. 
BY GL F. MATTHEW, M. A., F. R. S. C. 
'(Abstract from the Report of the Field Meeting held in July, 1886; read 5th 
October, 1886.) 
The fish remains of the Silurian age are of two different 
kinds, one consisting of small spines with fluted surfaces, which 
resemble those borne by certain sharks and by siluroid fishes. 
The second consisting of oval and rectilinear plates or shields, 
with curved surfaces, and which from their form and appear- 
ance are not easily recognized as parts of fishes. These plates 
covered the head and the anterior parts of the body, while the 
posterior part was protected by scales only, or entirely unarmed. 
Hitherto all the fishes of this family (Pteraspidae) have been 
spoken of as haying plates on the head, back and sides only, 
but the one I am about to describe had ventral plates as well, 
and in this respect corresponds to the remarkable armoured 
fishes of the Devonian age. 
The most obvious character by which these Silurian fish 
plates can be recognized is a fine but very distinct ridging of 
the surface, the details of the ornamentation being governed 
by the position of the plate in the series of plates with which 
the body was covered. 
The accompanying woodcut shows the outlines of these 
plates: 
Covering plates of Diplasp's Acadica (n. gen.) 
