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 shell, 
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 smal] remains have a specific difference. 
