129 
AMMONITES Duncani. 
TAB. CLVII. 
Spec. Cuan. Depressed; inner whorls partly ex- 
posed ; radii numerous, undulated ; edge flat, 
bounded by two rows of tubercles in the in- 
terior whorls ; a few tubercles occur upon the 
sides of the inner whorls: aperture ovato- 
sagittate. 
ae 
Taz radii are irregularly furcate, and more or less 
obscure about the middle of the sides: the tubercles on 
the interior whorls extend over the ends. of two radii, 
but on the external whorls they are little more than 
swellings of the ends of the radii: the greatest diameter 
is about twice the length of the aperture and four times 
the thickness. 
There is a peculiar elegance in this species that makes 
us regret its rarity, and the little chance we conse- 
quently have of seeing the exterior. The double row of 
button-like protuberances on either side the flattened 
outer edge, shewing the place of the siphuncle in the 
center, gives an appearance similar to that of some other 
species. The fine sharpness of the sinuated edges of the 
septa is beautiful. It has protuberating vermicule-like 
risings about it which interrupt the distinction of the 
whorls :—or are they stalagmitical droppings of pyrites ? 
It is partly chalky on the outside, perhaps owing to the 
decomposition of the calcareous shell; the rest is pyri- 
taceous except a little marle. It is from the forest or 
fen clay which runs through England from Weymouth 
to the wash of Lincolnshire, and was found by John and 
Philip Duncan, Esqrs. after whom I am pleased that it 
is named, at St. Neotts, Huntingdonshire. 
VOL. 1. 79/7 
