22 
Clealand, Esq, there is also a very good one in the 
British Museum ; the former is selected for a figure. I 
have one that exhibits a near approach to the external 
form of the shell, but would not make so handsome a 
figure ; it has in one part a small portion even of the 
shell itself remaining; none of its joints are free : on 
one side of it are several young Oysters, and on the 
other, a full grown Oyster, (Ostrea Delta) they adhere 
so closely, that there does not appear to be space enough 
between them and the stony cast for any shell, it 
must have been thin, and is perhaps of such a texture 
as does not permit it to be readily distinguished from 
the Oyster ; or we must conclude that the Ammonite 
was in a fossil state before the Oysters existed, but had 
not been removed far from its original station, before it 
was again buried to form along with the Oysters the in- 
dex to another epocha. This is the species referred to 
at page 72 of Vol. IV. as resembling the A. perarmatus. 
Found imbedded in sand in Marcham Field, near 
Abingdon, in Berkshire ; parts sometimes occur that 
must have belonged to shells above a foot in diameter. 
Casts of A. perarmatus tab. 352, in a similar loose 
state of preservation, are found accompanying the A. 
catena, and until lately, have been confounded with it : 
the ribs that connect the tubercles in pairs will distin- 
guish them ; such ribs being very rare upon the smaller 
spined A. Catena. 
