454 



V. Some species of fossil animals (pentacrinita) occur in the LIAS, and 



are not, I believe, seen in any of the succeeding superior strata, 

 but a recent similar animal is found in our present seas. 



VI. Some fossil animals (ammonites) are first seen in the LIAS and 

 appear in most of the succeeding strata, but appear to have 

 become extinct in the ocean which deposited the hard chalk. 



VII. Some fossils (bekmnitte) appear in the early strata, and are 

 continued upwards to the SOFT CHALK stratum, after which they 

 are not seen. 



VIII. Some fossils (oval ammonites, scaphittz, Sfc.) are not known in the 

 early strata, but occur in the HARD CHALK, and are not seen after- 

 wards: as if they had been created at a comparatively late 

 period, and had been soon afterwards suffered to become extinct. 



IX. Some fossil shells (trigonitce) are found in the LIAS and in MOST 

 OF THE SUCCEEDING STRATA,, and sometimes, but very rarely, in 

 the hard chalk. After this they are not seen in the remaining 

 superior strata, but of late years one species has been found in 

 our present seas. This however requires some explanation. 

 The trigonita are shells differing materially from any others in 

 the structure of the hinge, and obtain therefrom the most decided 

 generic characters. Until lately no shell of this genus was 

 known in a recent state : one however has been found by 

 M. Peron, in the South Seas ; but this shell, although really of 

 this genus, is of a different species from any shell, which has 

 been found in a fossil state. So that none of the species of shells 

 of this genus, which are known in a fossil state, have, in fact, 

 been found in any stratum above the hard chalk, or in our pre- 

 sent seas. 



X. In the SAND and in the BLUE CLAY above the chalk, many species 



of shells occur, of which not one is to be seen in the preceding 

 strata ; but of which several approximate to those in the present 

 seas. 



