14 
This species is from | to § an inch square, it has a 
brownish smooth epidermis, marked with distant concentric 
striae, and is pearly within. 
Many masses of these Shells have been found, each as 
big as a bushel or more, chiefly in a rotting state, in a 
mixed darkish Clay in different parts of Highgate Hill* 
but they are difficult to preserve. 
The right hand lower figure shows a fine specimen on a 
piece of Septarium of hardish brown Marie, with some 
fragments more or less enveloped in it. The figure of the 
inside near it is as distinct as I could make it with the help 
of many specimens, which all have a pearly appearance 
and lustre, both inside and out, when the epidermis is 
decayed. The upper figure shows a specimen of the same 
stone in a state of decay, full of smaller Shells; the outside 
has become ochraceous, and the Shells more chalky ; the 
inside being less changed is darker, and the remains of 
Shells more pearly. The two casts taken from within the 
Shells of this specimen (see the left hand figures) seem to 
show them to be nearly equivalved, but like the pcctens, 
the principal parts may be rather equal, while the wings of 
each valve do not meet each other. I do not know that this 
Shell has been discovered any where besides at Highgate. 
I have to thank Mr. Snow for this, among his other 
numerous favours, so likely to become instructive to the 
public. I have specimens of Avicula Hirundo from 
Marazion, found by Miss Elizabeth Pocock, and minute 
specimens from Bantry Bay in Ireland, by the friendship 
of Mr. Drummond, but it is certainly another species. I 
mention these here to show that we have still on our coasts 
Some Shells nearly allied to the fossil ones, which have 
frequently been considered as related more immediately to 
those of the East Indies. 
i 
