134 
A rude piece of Limestone from Dudley encloses this 
fragment; it is without the external shell, but the position 
of the siphunculus distinguishes it from all others that I 
have seen. I should not have figured this imperfect shelly 
had I not thought it convenient to particularize the differ-* 
ence of character in the shells belonging to certain rocks* 
for the sake of Geology, and even the more or less perfect 
preservation of the different subjects becomes of some conse- 
quence in such enquiries. In some instances we are pleased 
to find that such small remains have a specific difference. 
