282 LEPIDOID FISHES. 
Another family of these singular Fishes of the 
ancient world, which was exceedingly abundant 
in the Oolitic or Jurassic series, is that of the 
Lepidoids, a family still more remarkable than 
the Pycnodonts for their large rhomboidal bony 
scales, of great thickness, and covered with beau- 
tiful enamel. The Dapedium of the lias (PI. 1. 
Fig. 54.) affords an example of these scales, well 
known to geologists. They are usually furnished 
on their upper margin with a large process or 
hook, placed like the hook or peg near the upper 
margin of a tile ; this hook fits into a depression 
on the lower margin of the scales placed next 
above it. (See PI. 27, Figs. 3, 4, and PI. lo, Fig. 
17.) All Ganoidian Fishes, of every formation, 
prior to the Chalk, were enclosed in a similar 
cuirass, composed of bony scales, covered with 
enamel, and extending from the head to the rays 
of the tail.* One or two species only, having 
this peculiar armature of enamelled bony scales, 
rhicas Lupus, and other recent Fishes of different families. M. 
Agassiz observes, that it is a common fact, in the class of Fishes, 
to find nearly all the modifications which the teeth of these 
animals present, recurring- in several families, which in other re- 
spects are very different. 
* The Pycnodonts, as well as the fossil Sauroids, have ena- 
melled scales, but it is in the Lepidoids that scales of this 
kind are most highly developed. M. Agassiz has ascertained 
nearly 200 fossil species that had this kind of armour. The 
use of such an universal covering of thick bony and enamelled 
scales, surrounding like a cuirass the entire bodies of so many 
species of Fishes, in all formations anterior to the Cretaceous 
deposits, may have been to defend their bodies against waters 
