COPROLITES. 191 
The preservation of such foecal matter, and its 
conversion to the state of stone, result from the 
imperishable nature of the phosphate of lime, of 
which both bones, and the products of digested 
bones are equally composed. 
The skeleton of another Ichthyosaurus in the 
Oxford Museum, from the lias at Lyme Regis, 
(PI. 14) shows a large mass of fish scales, chiefly 
referrible to the Pholidophorus limbatus,* in- 
termixt with coprolite throughout the entire 
region of the ribs ; this mass is overlaid by many 
ribs, and although, in some degree perhaps, 
extended by pressure, it shows that the length 
* According to Professor Agassiz, the scales of Pholidophorus 
limbatus, a species very frequent among the fossils of the lias, are 
more abundant than those of any other fish in the Coprolites found 
in that formation at Lyme Regis ; and show that this species was 
the principal food of these reptiles. In Coprolites from the coal 
formation, near Edinburgh, he has also recognized the scales 
of Palaeoniscus, and of other fishes that are often found entire 
in strata that accompany the coal of that neighbourhood. 
Scales of the Zeus Lewisiensis, a fish discovered by Mr. Man- 
tell, in the chalk, occur in Coprolites derived from voracious 
fishes during the deposition of this formation. 
A Coprolite from the lias, (PI. 15, Fig. 3), remarkable for ils 
spiral convolutions, and vascular impressions, affords a striking 
example of the minute accuracy with which investigations are 
now conducted by naturalists, and of the kind of evidence which 
comparative anatomy contributes in aid of geological enquiry. 
On one side of this Coprolite, there is a small scale, (Fig. 3, a,) 
which I could only refer to some unknown fish, of the numerous 
species that occur in the lias. The instant I showed it to M. 
Agassiz, he not only pronounced its species to be the Pholido- 
phorus limbatus ; but at once declared the precise place which 
this scale had occupied upon the body of the fish. A minute 
