188 Dr Hibbert on the Limestone of Burdiehouse 



In reference to this most important portion of the structure of 

 the animal, the great orders of M. Agassiz'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 of 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. Agassiz 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.J, 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 Pal^eoniscus, the Am- 

 blypterus, and a new genus, to which M. Agassiz has given the 

 name of Eurynotus. 



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- 



