6 THE NATURAL HISTORY OF SELBORNE,. 
: LETTER III. 
The fossil shells of this district, and sorts of stone, such as 
have fallen within my observation, must not be passed over in 
silence. And first I must mention, as a great curiosity, a 
specimen that was ploughed up in the chalky fields, near the 
side of the down, and given to me for the singularity of its 
appearance; which, to an incurious eye, seems like a petrified 
fish of about four inches long, the cardo (or hinge) passing for 
a head and mouth. It is in reality a bivalve of the Linnzan 
Genus of Mytilus, and the species of Crista Gali; called by~ 
those who make collections, cock’s-comb. ‘Though I applied 
to several such in London, I never could meet with an entire 
specimen ; nor could I ever find in books any engraving from 
a perfect one. In the superb museum at Leicester House, 
permission was given me to examine for this article; and 
though I was disappointed as to the fossil, I was highly grati- 
fied with the sight of several of the shells themselves in high 
preservation. ‘This bivalve is only known to inhabit the Indian 
Ocean, where it fixes itself to a zoophyte, known by the name 
Gorgonia. ‘The curious foldings of the suture the one into the 
other, the alternate flutings or grooves, and the curved form of’ 
my specimen are much easier expressed by the pencil than by 
words. 
Ammonites [Cornua Ammonis| are common in this village. 
As we were cutting an inclining path up the Hanger, the 
laborers often found them on that steep, just under the soil, in 
the chalk, and of a considerable size. In the lane above Wall- 
head, in the way to Emshot, they abound in the bank in a 
darkish sort of marl, and are usually very small and soft: but 
in Clay’s Pond, a little farther on, at the end of the pit, where 
the soil is dug out for manure, I have occasionally observed 
them of large dimensions, perhaps fourteen or sixteen inches 
in diameter. But as these did not consist of firm stone, but 
