2 7 6 



HISTORICAL PALEONTOLOGY. 



of the Escharidce, the genera Eschar a and Escharina (fig. 193) 

 being particularly well represented. Most of the Cretaceous 

 Polyzoans are of small size, but some 7 attain considerable di- 

 mensions, and many simulate Corals in their general form and 

 appearance. 



The Lamp-shells (Brachiopods) have now reached a further 

 stage of the progressive decline, which they have been under- 

 going ever since the close of 

 the Palaeozoic period. Though 

 individually not rare, especially 

 in certain minor subdivisions 

 of the series, the number of 

 generic types has now be- 

 come distinctly diminished, the 

 principal forms belonging to 

 the genera Terebratula, Tere- 

 bratella (fig. 194), Terebratulina, 

 Rhynchonella, and Crania (fig. 

 195). In the last mentioned 



193. A small fragment of Escharina 

 Oceani, of the natural size ; and a portion 



of the same enlarged. Upper Greensand. of these> the shdl {s attache d 



to foreign bodies by the sub- 

 stance of one of the valves (the ventral), whilst the other or 

 free valve is more or less limpet-shaped. All the above-men- 

 tioned genera are in existence at the present day; and one 

 species namely, Terebratulina striata appears to be undis- 

 tinguishable from one now living the Terebratulina caput- 

 serpentis. 



Whilst the Lamp-shells are slowly declining, the Bivalves 

 (Lamellibranchs} are greatly developed, and are amongst the 



. 194. Terebratella Astieriana. Gault. 



most abundant and characteristic fossils of the Cretaceous 

 period. In the great river-deposit of the Wealden, the Bivalves 



