328 
THE GEOLOGIST. 
ON AN AMMONITE WITH ITS OPERCULUM IN SITU. 
By S. p. Woodward, F.G.S. 
Opercula of Ammonites are common in many localities, especially 
in banks and sections of the Kimmeridge Clay ; but they usually occur 
in broken fragments, and very rarely with their valves paired, unless 
sheltered within the last whirl of the shell to which they belonged. 
Even when thus protected the valves are generally displaced, as 
might be expected if we consider how slight is their union along the 
suture, and how great were the chances of being shifted by the con- 
traction of the animal after death, by the pressure of external mud. 
The British Museum contains several examples of Ammonites Jason, 
A. Brightii, A. jluduosus, A. lingulatus, and other species with their 
opercula more or less shifted ; and Mr. Charles Moore, of Bath, has 
several small shells of Ammonites planorliis from the Lower Lias, 
•with the opercula remaining in their true position ; the smallest in- 
dividual is only one quarter of an inch in diameter. 
I have recently obtained a specimen of Am- 
monites subradiafMs (J. Sby.) from Mr. Joseph 
Wood, an experienced collector (formerly of 
Bath, but now living at 23, New Union-street, 
Moorfields), who discovered it in the Inferior 
Oolite, of Dundry, near Bristol, with the oper- 
culum remaining in its natiiral position as 
represented in the accompanying figure. 
The shell measures sixteen lines by twelve 
and a half, with a maximum thickness of four and 
a half lines. It agrees with the ordinary run of 
specimens from Dundry, and differs from the 
Ammonites suhradiatus. 
example figured by Sowerby in being less com- '^-^ 
pressed, and more widely umbilicated ; the umbi- 
licus measures four lines across, and is bordered by a steep margin. 
The operculum is flat in the middle, with a slight furrow along 
the suture, and is much bent down at the hinder comers where it 
abuts against the inner whirl of the shell It is six lines long and 
four wide, and is sculptured externally with about twelve angulai 
concentric furrows ; the inner surface is smooth, as shewn by the 
fracture and removal of a portion. It closely resembles the opercula 
of Ammonites Brightii and A. lingnlatvs, to which A. suhradiatus is 
nearly related. 
British Museum, August, 1860. 
