150 INTESTINAL STRUCTURE OF ICHTHYOSAURUS. 



The preservation of such foccal 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 pro- 

 ducts 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 referable to the Pholido- 

 phorus, limbatus,* intermixed 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 of the stomach was nearly 

 co-extensive with the trunk. 



* 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 recognised the scales of Palseoniscus, and of other fishes that are 

 often found entire in strata that accompany the coal of that neighbourhood. 

 Scales of the Beryx armatus, a fish discovered by Mr. Mantell, in the chalk, 

 occur in Coprolites derived from voracious fishes during the deposition of 

 this formation. 



A Coprolite from the lias, (PI. 15, Eig. 3,) remarkable for its spiral 

 convolutions, and vascular impressions, affords a striking example of the 

 minute accuracy vv'ith which investigations are now conducted by natu- 

 ralists, and of the kind of evidence which comparative anatomy contri- 

 butes in aid of geological inquiry. On one side of this Coprolite, there is 

 a small scale, (Fig. 3, «,) wiiich 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 Pholidophorus 

 limbatus ; but at once declared tiic precise place which tiiis scAo had occu- 

 pied upon the body of the fish. A minute tube upon its inner surface, 

 (P!. 15, Fig. S',) scarcely visible without a microscope, showed it to have 

 been one of those which form the lateral line of perforated scales, that 

 pass from the head towards the tail, one on each side of every fish : 

 and convey a tube for the transmission of lubricating mucus from glands 

 in the head, to the extremity of the body. The place of the seals in this 

 line, had been on the left side, not far from the head. Fig. 3", is the 

 upper surface of a similar scale, showing at c tlie termination of the mucous 

 iuct. 



