TO GEOLOGY. 179 



M. 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&quot; very slightly thickened 

 and minutely crenulate within. 

 Length ll-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- 

 nellae, as it has characters which approach strongly to the 

 Volvarice. It has no thickened margin on the outer lip, at 

 least in the specimens (three) which I have seen. The 



