GEOGNOSY AND GEOLOGY. 175 
excrements. These are frequently found fossilized, and are known as 
coprolites. They contain teeth, scales, fins, and bones of fishes, in large 
number, which, together with the general structure of the animal itself, 
allow us to consider the Ichthyosaurus as highly destructive to the animals 
with which it was associated, and to fish especially. 
The Plesiosaurus is distinguished from the Ichthyosaurus by the posses- 
sion of a very long flexible neck, provided with a much smaller head. The 
paddles were also longer and the tail shorter: P. dolichodeirus (fig. 25°). 
The teeth (fig. 25") were conical and finely furrowed: P. macrocephalus 
(pl. 40, fig. 10). 
The Pterodactyles, or flying saurians, are among the most extraordinary 
forms, either recent or fossil, known to zoologists: Pterodactylus 
crassirostris (pl. 41, fig. 35). They had a large head with very broad 
orbits, and unjointed bony sclerotics. The broad jaws are provided with 
long subulate teeth, inserted in special sockets. The long strong neck is 
set on a short trunk, which ends posteriorly in a thin short tail. The 
humerus is short and thick, the fore-arm more than twice as long. Upon 
the carpus is set a hand with powerful claws, the external finger being very 
long and falcate. The hind feet were tolerably Jong, thin, and attached to 
a feeble pelvis. The hind and fore-feet were probably united by a 
membrane, as in the Cheiroptera or bats of the present day, admitting of 
feeble powers of flight. The principal difference in the structure of the 
wings of the pterodactyle and the bat lies in the fact, that while the former 
has but one finger greatly developed, the latter has four. 
The first traces of Mammalia are found in the Stonesfield slate, and 
probably belonged to carnivorous Marsupialia. Several genera and species 
have been distinguished, as Phascolotherium bucklandii (pl. 38, fig. 67, 
lower jaw). 
The Jurassic fresh water formations are in some places, as at Neufchatel, 
replaced by marine limestones and marls. Of the fossils peculiar to the 
Neocomien, some of the most interesting forms will now be mentioned. 
Of Echinodermata, Holaster complanatus (Spatangus retusus, pl. 39, 
jig. 13). The Holasters are cordiform, and possess curved ambulacral 
zones in the vicinity of the generative apparatus. The mouth is placed 
anteriorly on the lower side in a depression, the anus being situated behind 
and more towards the upper face. Other fossils of interest are Trigonia 
caudata (fig. 19), Mytilus simplex (fig. 28), Turbo plicatilis (fig. 35). 
Pleurotomaria neocomensis. The chambered cephalopods are represented 
by Crioceras, a genus characterized by its free turns: C. duvalii (fig. 38) ; 
also Ammonites macilentus ( fig. 40) ; Scaphites and Toxoceras distinguished 
from each other and from ammonites by the character of their rolling up: 
S. ivanii (fig. 42) and T. bituberculatus ( fig. 41). 
In surveying the fossils of the Jura we observe a great variety of forms, 
among which the Saurians stand pre-eminent. The central figure of 
pl. 37, after Buckland, illustrates the extraordinary character and probable 
rapacity of some of the animals characteristic of the lias. In this representa- 
tion @ indicates the Ichthyosaurus communis; b I. longirostris about tc 
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