242 PICTURESQUE SKETCHES 



are frequently found in the chalk, but which has 

 no living representative. It often attained a large 



Fig. 98 Fig. 99 



TRIGONIA. PLICATULA. 



size, and its hinges being singularly thick and pon- 

 derous, while the shell was often thin, it is not un- 

 common to find fragments of the more solid portion 

 detached. The Trigonia (fig. 98) is the ancient 

 representative of a genus still found, and not uncom- 



Fig. 100 



TEREBRATULA. 



INOCERAMUS. 



mon on the coast of Australia, but now absent from 

 the northern hemisphere ; and the other, Plicatula 

 (fig. 99), is one of a larger group, nearly allied to 

 the oyster, and very common throughout the creta- 



