188 Dr Hiszerr on the Limestone of Burdiehouse 
In reference to this most important portion of the structure of 
the animal, the great orders of M. Acassiz’s system are founded. 
The remains of such fish discovered at Burdiehouse as I in- 
tend to notice in the present memoir, are referable to two of these 
orders. 
The first uf these orders includes Placoidian fish. They are 
distinguished by the irregularity manifested in the solid parts of 
their integuments, which consist of materials of enamel often con- 
siderable, or sometimes reduced to little points ; as, for instance, 
the tubercles of rays, or the different chagrins of squali, &c. 
To this order M. Acassiz has referred the fish to which 
certain bony rays of gigantic dimensions found at Burdiehouse 
belong. The animal is supposed to have approached the Ces- 
tracion of modern times ; which fish is the type of the family of 
Cestraciontes. He conceives that the remains in question may 
be referred to a new genus, to which he has given the name of 
GYRACANTHUS FORMOSUS. 
Other relics are referred to fish of a second or Ganoidian or- 
der, distinguished by the angular, rhomboidal or polygonal scales, 
which they possess in common ; these scales being at the same 
time formed of bony plates, and covered over with enamel. This 
order includes various families, but, in reference to the fossil re- 
mains of Burdiehouse, two only of them will have to be consi- 
dered. 
To the family of Lepidoids (Agass.), which are characterised 
by teeth after the form of a brush disposed in several rows, or in 
one single row of small obtuse teeth, three genera discovered at 
Burdiehouse have been assigned, viz. the PaLmontscus, the Am- 
BLYPTERUS, and a new genus, to which M. Acassiz has given the 
name of Eurynorus. 
To the family of Sauroids, which are distinguished by conical 
and pointed teeth, alternating with small teeth en brosse, by flat 
scales, rhomboidal and parallel to the body, which is entirely co- 
