[The 10th. ] THE VARIOUS EXPLANATIONS. 429 
Trionychidae, distinguished by their long neck, and a broad car- 
tilaginous margin to the small back-shell, appears first in the 
wealden. No traces occur of it in any subsequent formation, till 
the present period, when we find it represented by the large and 
savage inhabitants of the Mississipi, the Nile, and the Ganges.” 
“What is still more to the purpose is, that the /guanodon, a 
vast saurian which was contemporary with the Plesiosaur and 
Ichthyosaur, though transmitting no observed representative of its 
form through the tertiary era, is yet well represented by the 
existing guanadae of the American tropics.” 
“Tt is true the /guana is not an /guanodon; but the forms are 
closely allied. I do not suppose that the so-called sea-serpent is an 
actual Plesiosaur, but an animal bearing a similar relation to that 
ancient type. The /guanodon has degenerated (I speak of the type, 
and not of the species) to the small size of the /guana; the Ple- 
siosaurus may have become developed to the pein dimensions 
of the sea-serpent.” 
“A correspondent of the Zoologist (2395) adduces the great au- 
thority of Professor Agassiz to the possibility of the present exis- 
tence of the Hnalosaurian type. That eminent palaeontologist is 
represented as saying, that “it would be in precise conformity 
with analogy that such an animal should exist in the American 
seas, as he had found numerous instances in which the fossil forms 
of the Old World were represented by living types in the New. 
He instances the gar pike of the Western rivers, and said he had 
found several instances in his visit to Lake Superior, where he 
had detected several fishes belonging to genera now extinct in 
Kurope.”” 
“On this pomt, however, an actuall testimony exists, to which 
I cannot but attach a very great value.” 
Here Mr. Gossr cites the report of Captain Horr (n°. 119), 
and goes on: 
“Now, unless this officer was egregiously deceived, he saw an 
animal which could have been no other than an nae a 
a marine reptile of large size, of sauroid figure, with turtle-like 
paddles. It is a pity that no estimate, even approximate, of the 
dimensions is given; but as the alligator affords the comparison as 
to form, it is most probable that there was a general agreement 
with it in size. This might make it some twelve or fifteen feet 
in length.” 
“I cannot, then, admit that either the general substitution of 
