TO GEOLOGY. 179 
JM. ovata. Plate 6. Fig. 191. 
Description. Shell ovate, smooth; substance of the 
shell thick ; spire very short, the apex being scarcely visi- 
ble ; whorls flattened above ; columella with eight folds ; 
mouth narrow, curved ; outer lip very slightly thickened 
and minutely crenulate within. 
Length 11-20ths, Breadth .3, of an inch. 
Observations. ‘This species most resembles the last de- 
scribed, but differs in the spire, in the number of folds, and 
in the size. In the adult the last whorl covers the spire 
except at the very apex. The thickening of the margin 
of the outer lip is so small as scarcely to be perceptible. 
In some individuals it cannot be traced. This lip is edged 
and somewhat gibbous above. 
M. incurva. Plate 6. Fig. 192. 
Description. Shell ovate, smooth ; substance of the 
shell thin; spire somewhat protruded, rounded at the 
apex ; whorls four, flattened above; columella curved, 
with four folds ; mouth subovate, narrow ; outer lip sharp. 
Length 5-20ths, Breadth nearly 3-20ths, of an inch. 
Observations. This is placed at the last of the Margi- 
nelle, as it has characters which approach strongly to the 
Volvarie. It has no thickened margin on the outer lip, at 
least in the specimens (three) which I have seen. The 
