WSSIL MOLLUSC A. 273 



but univalve and bivalve mollusca, such as Vohita 

 nodosa^ P hones exieiisus, Rostellaria mnpla, Leda 

 amygdaloides, Cryptodon, etc., are found at Highgate. 

 Some of these, and other fossils, are also met with near 

 Hungerford, Basingstoke, Bognor, Finchley, Holloway, 

 Ipswich, and Harwich ; especially in the cement stones, 

 which, near Harwich and Ipswich, are often full of 

 Modiola and Cyrena. The Harwich cement-stones 

 are rich in fossil wood, showing structure when cut 

 and polished ; and large fragments of this wood are 

 often seen perforated and honey-combed by a species 



Fig. 261. — Wood perforated by the tubes of Teredo. 



of the same kind of boring-mollusc {Teredo) as that 

 which has earned for itself the modern name of " ship- 

 worm." In the Suffolk crags, the bewildered student 

 frequently finds contorted and serpentinely inter- 

 twined masses, and he wonders what they are, little 

 thinking they are the filled-up 7Vr^^d?-borings in the 

 fossil woods of the London Clay. The fossil wood 

 was washed out of the latter deposit by denudation, 

 was then gradually dissolved away, so that eventually 



T 



