44 
strie of different widths, relieved by a more or less beautiful 
nearly white china-like ground. The insides are all so 
lined with marle or crystallized Carbonate of Lime, that the 
teeth of the hinge cannot be seen. 
TAB. XIV.—Left hand middle figure. 
This much resembles the last, and is probably only a va- 
riety of it, but it differs in being apparently quite smooth, 
to the unassisted eye, it is however striated ; there are a few 
broadish concentric lines of a light brown colour on the 
shell, which is otherwise almost white ; it is rather a gib- 
bous shell. The pair figured were found exposed on a 
darkish brown marly piece of Septarium from the Highgate 
Clay stratum. 
TAB. XIV.—Right hand middle figure 
much resembles the last, but is smoother on the most pro- 
minent part of the shell, and does not shine so brightly: it 
is rather flatter, and nearly of an uniform light brown co- 
Jour. This is in a more sandy Septarium from Highgate. 
TAB. XIV.—Left hand lower figure. 
The only material difference between this and the three fore- 
going, is its more rhomboidal appearance, though it is pro- 
portionally rather longer. It is rather paler in colour than 
the last.. Also from Highgate. 
The four specimens last described are probably only 
varieties of each other; I have, however, met with some 
who consider them as distinct species. 
