104 THE MOLLUSCA 



The Keyhole Limpets and the Split Limpets have limpet-like 

 shells, but the first are distinguished by a small hole at or near 

 the apex, and the second by a slit of varying length in the margin 

 of the shell. Through these apertures the water escapes after it 

 has bathed and aerated the gills below. 



The Ormer or Ear Shell (Haliotis) has a series of perforations 

 on the margin of the shell through which the water passes, and 

 the mollusc protrudes delicate filaments that wave about in the 

 water and so keep up a constant circulation. The Ormer clings 

 to the rocks with its great foot as tenaciously as a limpet, and 

 is just as dull-looking in outward appearance ; but the shells have 

 a most beautiful lining of mother-of-pearl, which is much used 

 for inlaid work and the manufacture of ornaments. The Ormer is 

 found in most parts of the world, with the exception of South 

 America, but the only British species occurs in the Channel 

 Isles, where it is fairly common on stones and rocks in low rock 

 pools. 



The American Slipper or Chain Limpet (Crepidula fornicata) is 

 one of the most curious of the limpet-form shells. Its remarkable 

 life-history has been described by Mr. J. H. Orton, B.Sc., as 

 follows: "Crepidula spawn during the period from early March 

 to the beginning of November, but the greater number of 

 individuals appear to spawn about May. This limpet takes 

 special care of its spawn. It constructs about fifty to sixty 

 membranous bags, into each of which it passes about 250 eggs, 

 and as the bags are made and filled with eggs they are closed and 

 fastened together by short cords. These cords are finally all stuck 

 on to the surface on which the Slipper Limpet happens to be 

 sitting, so that by taking away the spawning individual the 

 spawn is uncovered ; it looks like a bundle of balloons, each 

 containing a number of eggs. 



" The eggs are protected by the mother Crepidula for almost 

 a month, but about the end of the month holes appear in the egg- 

 bags, and the developing Crepidulae escape by swimming away 

 from their parent. 



"After a short free - swimming period, the young limpets 

 settle down on some convenient shell, and there they remain for 

 the rest of their lives. They habitually attach themselves to one 

 another, so that regular chains of Slipper Limpets, each one fixed 



