44 
striae of different widths, relieved by a more or less beautiful 
nearly white china-like ground. The insides are all so 
lined with marie 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- 
lour. This is in a more sandy Septarium from Highgate, 
TAB. XIV .—Left hand lower figure . 
The only material difference between this apd the three fore- 
going, is its more rhomboidal appearance, though it is pro- 
portionally rather lopger. 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. 
