216 Dr Hiszerr on the Limestone of Burdiehouse, 
During the same year (1834) scales of the Megalichthys were shewn to me by 
W. C. Trevetyan, Esq. of Wallington, which he had obtained from the coal-fields 
of Northumberland. 
As these remarks conclude my account of the Megalichthys, I may here mention 
the information which M. Acassiz communicates to me, that in the much newer 
formation of Whitby and Scarborough, he has found the fragments of a fish which 
even exceed in size those of the Burdichouse animal; some of the portions of the 
cranium being nearly two feet in diameter. In announcing to me the discovery of 
this monster, he adds, ‘* After having seen so many extraordinary and surprising things 
in the monster of Whitby, which exceeds the largest Ichthyosaurus, I perceive that I 
am still only commencing the preface of a book, which future years will supply with 
the wonders of the sea. And I shall think myself happy if I can only have excited 
interest for a study, which is still so difficult for want of terms of comparison suffi- 
ciently numerous.” 
SECTION XIII—THE GENUS OF PYGOPTERUS BELONGING TO THE SAUROID 
FAMILY. 
While the primeval waters of the carboniferous epoch had 
their larger sauroid monsters, they had also lesser sauroid tribu- 
taries, one of which was in the form of the Pygopterus, belonging 
to the same family as that to which the Megalichthys has been 
referred. 
M. Acassiz has favoured me with the following description 
of the Pygopterus of Burdiehouse. Unfortunately, however, it 
only applies to a fragment of the fossil fish, which is represented 
in Plate VII. fig. 2. 
‘The proportions of the rigid tail of the animal, the relative posi- 
tion of the dorsal and of the anal fins, the form of the fins, which 
are horizontally and perpendicularly elongated, as well as the 
considerable number of rays which compose them, serve to point 
out the posterior part of a fish of the genus Pygopterus, which 
belongs to the “Sauroides Heterocerques,” (Acass.) Amidst the 
numerous fragments of bones of the head, as well as of the thoracic 
cincture, which have been found along with them, it will remain 
for a detailed description to explain, by the system of exclusions, 
what might have belonged to the animal. M. Acassrz then 
conceives, from his having seen so many heads of the Pygopterus, 
6 
