IN DESCRIBING SHELLS. 39 



Posticum is when the partition is at the back part of the inside, 

 as in Patella Porcellana. 



OF THE OPERCULUM. 



Linnaeus scarcely mentions any of the opercida: Rumphius 

 and Gualtieri have given figures of several of them ; most of 

 the Turbines have thick testaceous opercida exactly closing the 

 aperture, and so have most of the Neritce ; but these are not in 

 general quite so thick as those of the Turbines,h\ii they also take 

 the shape of the mouth of their respective shells ; very few of 

 the Helices have any, except Helix vivipara and tentaculata ; 

 those are thin and horny, and exactly fit the aperture. Several 

 Buccina, Murices, and Coni, &c. have also opercida, but these 

 extend in size to only a part of the aperture. 



OF THE SURFACE OF SHELLS, SUPERFICIES. 



Licevis is when the surface is smooth and even, as in Mactra 



stultorum and Voluta porphyria. 

 Lifsvigata is as if worn or washed smooth, as in Tellina Icevi- 



gata and Buccinum decussatum. 

 Glabra is with the outside bright, as Venus Meretrix and 



Conus Capitaneus. 

 Glaberrima is very bright, as Venus castrensis and Bucqinum 



glabratum.. 

 Nitida is shining, as Tellina radiata and Turbo petholatus. 

 Lineatis is marked with coloured lin€s, as in Conus Princeps. 



