in the Neighbourhood of Edinburgh. 217 
as well as the head of the Megalichthys of Leeds, that the iden- 
tification will not be insurmountable. 
This relic was the first which I discovered at Burdiehouse ; 
for which reason I have requested M. Acass1z, that, in its specific 
name, I may be allowed to dedicate it to a geologist for whom I 
‘possess the greatest esteem. He has accordingly obliged me by 
sanctioning the name of Prcorrerus Buckianpt. 
M. Acassiz conceives that the best specific character of the 
Pygopterus Bucklandi is the relative smallness of its scales. 
SECTION XIV—THE REMAINS OF THE FISH OF THE PLACOIDIAN ORDER 
DISCOVERED AT BURDIEHOUSE. 
It has been explained, that Placoidian fish are easily known on 
account of the irregularity manifested by the solid parts of their 
integuments, which consist of materials of enamel sometimes con- 
siderable, and sometimes reduced to little points ; as is shewn in 
the tubercles of Rays, or in the different chagrins of Squali, &c. 
The same naturalist, at the commencement of his great work, 
has expressed his imperfect knowledge of the fossil fish of this 
order. But I believe that since his recent visit to Great Britain, 
he has been enabled to examine some few specimens in compara- 
tively a better state of preservation. He conceives, that, in cor- 
respondence with differences of organization, such remains of fish 
as are found in beds anterior to the carboniferous group, would 
have to be referred to the order of Placoids. 
M. Aceassiz has recently stated, that, among the Placoids, 
those above all predominate which have their teeth furrowed in 
both the external and internal surface, and have large thorny rays. 
These large rays are now considered as the supports of the 
dorsal fins of several genera, which, from their approach to the 
Cestracion of New Holland, M. Acassiz has formed into a dis- 
tinct family, under the name of Cestraciontes, to which family six 
fossil genera, approaching to the Squalus, with rays differing con- 
siderably from each other, have been already assigned. 
VOL. XIII. PART I. Ee 
