56 
bersare then generally filled or lined with quartz crystals. 
I have several large fragments of nearly such from the 
neighbourhood of Fonthill, Wilts. A specimen from the 
last place in flint I have figured in British Mineralogy, 
tab. 310.; it is composed of calcedony, which has 
formed a thin coat over the shell, septa and all, 
when the shell decaying has left the calcedony with its 
exact form. It has been said, somewhere, that Mr. 
Beckford, of Fonthill, w as in possession of one, holding 
Feldspar; upon enquiry I have every reason to think 
this to ha ve been a mistake ; if such a one w as at Fonthill, 
Mr. Beckford was so kind as to order it to be sent to me, 
but no such thing existed. The half of one, how- 
ever, the smaller chambers of which are lined with 
inverse rhombs of Carbonate of Lime supporting short 
prismatic crystals of the same substance, was added 
to my collection ; it is from Chicksgrove quarry, one 
mile and a quarter E. N. E. of Tisbury, near Hin- 
don, Wilts, and measures two feet three inches ill 
diameter. When I was at that place some years ago, 
the quarry men told me, that they had broken within 
that week, one as large as the hinder wheel of a coach l 
Lister says his was two feet, and there is in the museum 
at Paris, a shell of the same genus four feet in diameter ; 
knowing this, Montfort seems ready to give credit to the 
assertion, that they are sometimes eight feet. The 
Chicksgrove one just mentioned is the largest I have met 
with ; it is the var. a and in a compact sandy Limestone ; 
there is part of a curiously formed crab’s claw in the stone, 
and a number of plain serpulse about the mouth of the 
shell ; there is a specimen of this variety a, brought from 
Purbeck Isle, as it is called, in Dorsetshire, measuring 
21 inches in diameter, to be seen in the basement, in front 
«of one of the warehouses in the London Docks. 
