MOLLUSCS 87 



are exclusively vegetarian, feeding chiefly at night and 

 returning to the spot they usually occupy by day with a 

 remarkable persistence that bespeaks a noteworthy sense 

 of orientation. The shell of our own species varies 

 greatly with the locality, and experts can even tell which 

 point of the compass the creature habitually faces by its 

 formation. In the larval stages the limpet has the nucleus 

 of a spirally-twisted shell, suggesting that its shelly home 

 has acquired the well-known" Chinaman's hat " shape in 

 conformation with its peculiar way of life, the flattened 

 conical form being best suited to withstand the fury of the 

 waves. 



The Ear Shells or Ormers (Haliotis) are familiar to all 

 as ornaments. The shell has a series of openings along the 

 thickened margin and through these tactile organs are 

 protruded. Like all shell-bearing molluscs the Ormer 

 enlarges its shell to accommodate its increasing size by 

 continually adding layers of cement to the outer margin. 

 Since the Ormer requires but five orifices for the extrusion 

 of its feelers, those no longer required are sealed up with 

 shelly material as occasion arises. Ormers reach their 

 maximum size in tropic seas and both shell and animal 

 are in great demand, the one for ornament and the other 

 as a comestible. The animal holds the speed record 

 for Gastropod molluscs, the common species still found 

 in the Channel Islands gliding along at the rate of several 

 feet a minute. 



The Top Shells (Trocbus, etc.), like the Ormers, line 

 their shells with mother of pearl, and in consequence have 

 always been in great demand for ornamental purposes of 

 every description. As with most molluscs the largest 



