All Operculum from the Lily dale Limestone. 155 



relations of these shells. One thing appears pretty clear, shells 

 similar to O. Northi are not referable to Euoinphalus., or any of 

 its allies, as recently defined by the late Prof. L. G. DeKoninck, 

 nor, so far as I am aware is the operculum of this group known 

 with any certainty, although DeKoninck surmised that the 

 peculiar bodies described by him, under the name of Hypode7na, 

 might occupy this relation to ' Euomphalus. If so, the divergence 

 of shells like our O. Northi from the latter is all the greater. 



DESCRIPTION OF PLATE IX. 



Fig. 1. — Exterior of operculum. 

 ,, 2. — Interior ,, ,, 



,, 3. — Thin transverse section prepared for the microscope. 

 ,, 4. — Longitudinal ,, ,, ,, ,, 



The figures are twice the natural size. 



