ppermost layer (Laramie) we find
traces of a last curious expansion--the group of horned reptiles, of the
Triceratops type, which we described as the last of the great
reptiles. The Ichthyosaurs and Plesiosaurs vanish from the waters. The
"sea-serpents" (Mososaurs) pass away without a survivor. The flying
dragons, large and small, become entirely extinct. Only crocodiles,
lizards, turtle, and snakes cross the threshold of the Tertiary Era. In
one single region of America (Puerco beds) some of the great reptiles
seem to be making a last stand against the advancing enemy in the dawn
of the Tertiary Era, but the exact date of the beds is disputed, and
in any case their fight is soon over. Something has slain the most
formidable race that the earth had yet known, in spite of its marvellous
adaptation to different environments in its innumerable branches.

We turn to the seas, and find an equal carnage among some of its most
advanced inhabitants. The great cuttlefish-like Belemnites and the whole
race of the Ammonites, large and small, are banished from the earth. The
fall of the Ammonites is particularly interesting, and has inspired
much more or less fantastic speculation. The shells begin to assume such
strange forms that observers speak occasionally of the "convulsions" or
"death-contortions" of the expiring race. Some of the coiled shells take
on a spiral form, like that of a snail's shell. Some uncoil the shell,
and seem to be returning toward the primitive type. A rich eccentricity
of frills and ornamentation is found more or less throughout the whole
race. But every device--if we may so regard these changes--is useless,
and the devastating agency of the Cretaceous, whatever it was, removes
the Ammonites and Belemnites from the scene. The Mollusc world, like the
world of plants and of reptiles, approaches its modern aspect.

In the fish world, too, there is an effective selection in the course of
the Cretaceous. All the fishes of modern times, except the large
family of the sharks, rays, skates, and dog-fishes (Elasmobranchs), the
sturgeon and chimaera, the mud-fishes, and a very few other types, are
Teleosts, or bony-framed fishes--the others having cartilaginous frames.
None of the Teleosts had appeared until the end of the Jurassic. They
now, like the flowering plants on land, not only herald the new age,
but rapidly oust the other fishes, except the unconquerable shark. They
gradually approach the familiar types o