202 
same in a red ferruginous stone, with specimens of which 
G. B. Greenough, Esq. has kindly supplied me. 
Figures 2, 3, 4, and 5, show the growth of the smaller 
variety, of which the youngest is not at all plaited: as they 
advance they also become more gibbous. ‘They are found 
in immense numbers in the green sand of Warminster, and 
the neighborhood of Longleat, Chute Farm, &c.: they 
have lost more of the recent shell-like appearance than the 
above, and are occasionally silicified, the green sand stick- 
ing about them. 
These seem to join the T. intermedia, which is found in 
the same neighborhood; see Tab. 15, Fig. 8. 
