PLATE 7. 
UNIVALVE SHELLS. LIMESTONE, 
FIG. I, 2. 
CONCHYLIOLITHUS Helicites (Catillus) depres- 
sus, subtus planus, supra concavus contractior, 
ambitu obtuso lato obliquo : marginibus acutis. 
S. p. 
A fossil shell — ^The original an Helix — Depressed ; be- 
neath nearly flat ; above concave, somewhat contracted ; 
crossed with oblique striae. The volutions about three. The 
ambit, or back of the outward whirl, broad, convex, 
oblique, transversely striated, and bordered on each side 
by a sharp edge or margin. 
This species is pretty frequent — It is to be met with in 
the limestone near Tideswdl, Winster, and other places — 
And I have lately observed it at Buxton, very much flat- 
tened or compressed, in the shale, which interposes between 
the limestone and gritstone strata of this county. 
Fig. 1. Full view of the concave or dish-like side. This, 
as above remarked, is smaller or more contracted than the 
opposite side of the shell. Hence, Its margin, when viewed 
as in the present figure, has the appearance of a sharp ridge 
down the centre of the outward volution. 
D 
