166 
THE GEOLOGICAL MIDDLE AGE. 
in some of the Lobsters we have the first advance 
towards the highest class of Crustacea in the ex- 
pansion of the transverse diameter now so charac- 
teristic of the Crabs. Among Mollusks we have 
a host of gigantic Ammonites ; and the naked 
Cephalopods, which were in later times to become 
the prominent representatives of that class, al- 
ready begin to make their appearance. Among 
Radiates, some of the higher kinds of Echino- 
derms, the Ophiurans, and Ecliinoids, take the 
place of the Crinoids, and the Acalephian Ccrals 
give way to the Astrsean and Meandrina-like 
types, resembling the Reef-Builders of the pt es- 
ent time. 
I have spoken especially of the inhabitants of the 
Jurassic sea lying between England and France, 
because it was there that were first found the re- 
mains of some of the most remarkable and largest 
Jurassic animals. But wherever these deposits 
have been investigated, the remains contained in 
them reveal the same organic character, though, 
of course, we find the land Reptiles only where 
there happen to have been marshes, the aquatic 
Saurians wherever large estuaries or bays gave 
them an opportunity of coming in near shore, so 
that their bones were preserved in the accumula- 
tions of mud or clay constantly collecting in such 
localities, — the Crustacea, Shells, or Sea-Urchins 
