XVI 
INTRODUCTION. 
Amiidce. 
The separation of the Amiidae from the Eugnathidse is perhaps 
arbitrary, but it is at least convenient. The genus Eurycormus, 
with cycloidal scales and ring-vertebrae, may be as appropriately 
placed in one family as in the other; so also may the small noto¬ 
chordal fishes named Liode-smus. The former, however, is assigned 
to the Eugnathidae because it exhibits fulcra ou the fins; the latter 
to the Amiidae, because all its fins seem to be destitute of fulcra. 
Amici itself does not date back beyond the Upper Eocene, but the 
extinct species and possibly allied genera are very unsatisfactorily 
known, owing to the fragmentary nature of the fossils. Never¬ 
theless, the vertebral centra are so characteristic that it is possible 
to obtain considerable information as to its former range; and the 
interesting result is arrived at, that Amia (or fishes represented by 
fragments indistinguishable from it) was distributed throughout 
Western Europe in the Eocene period, and survived in some areas 
so late as the Lower Miocene. The supposed Amioid from the 
Miocene of Oeningen, Switzerland, proves to have been wrongly 
determined, and is a truly “ Teleostean ” fish. 
Pachycormidce. 
A remarkable modification of the thin-scaled type of Eugnathidae 
suddenly appears in the Upper Lias. The segments of the axial 
skeleton of the trunk multiply considerably ; the rostrum begins to 
project and prevents the premaxillae from meeting in the middle 
line; while the fins, especially the pectorals and caudal, are adapted 
for rapid progression. This modification, in fact, eventually results 
in genera having the outward form of the modern “ sword-fishes ” ; 
and they are particularly interesting as showing how the Proto- 
spondylic type of axial skeleton may be modified to produce the 
same mechanical effect as a robust chain of vertebrae terminated 
behind by its complex hypural bone. All these fishes are proved 
to have had a persistent notochord, and it is not improbably to com¬ 
pensate for this weakness that the segments of the axial skeleton 
are so remakably shortened and multiplied. In most genera also 
a single, much-expanded haemal arch has been observed at the base 
of the lower lobe of the powerful, deeply-forked tail; this admir¬ 
ably serving the purpose of a hypural, and yet not fundamentally 
altering the normal “ stegurous ” tail such as characterizes all 
Protospondyli. 
