74 THE OLD RED SANDSTONE. 
which, like those of the Dipterus, were placed fronting each 
other, and in pairs. But the head, in proportion to the body, 
was in greater size than in either the Dipterus or Osteolepis ; 
and the mouth, as indicated by the creature’s length of jaw, 
must have been of much greater width. In their more strik- 
ing characteristics, however, the three genera seem to have 
nearly agreed. In all alike, scales of bone glisten with en- 
amel; their jaws, enamel without and bone within, bristle 
thick with sharp-pointed teeth; closely-jointed plates, bur- 
nished like ancient helmets, cover their heads, and seem to 
have formed a kind of outer table to skulls externally of bone 
and internally of cartilage ; their gill-covers consist each of 
a single piece, like the gill-cover of the sturgeon; their. tails 
were formed chiefly on the lower side of their bodies; and 
the rays of their fins, enamelled like their plates and their 
scales, stand up over the connecting membrane, like the steel 
or brass in that peculiar armor of the middle ages, whose 
multitudinous pieces of metal were fastened together on a 
groundwork of cloth or of leather. All their scales, plates, 
and rays present a similar style of ornament. The shining 
and polished enamel is mottled with thickly-set punctures, or, 
rather, punctulated markings; so that a scale or plate, when 
viewed through a microscope, reminds one of the cover of a 
saddle. Some of the ganoid scales of Burdie House present 
surfaces similarly punctulated.* 
* There exists, according to Agassiz, only a single species of Dip- 
terus — D. macrelepidotus ; whereas four species of Diplopterus have been 
enumerated — D. affinis, D. borealis, D. macrocephalus, and D, Agassizii. 
The existence of the last named, however, as a distinct species, is re- 
garded as problematical by the distinguished naturalist whose name 
has been affixed to it. 
