MOLLUSCS 97 



according to the arrangement of the gills, the orders being 

 known as Protobranchia, Filibranchia, Eulamellibranchia and 

 Septibranchia. 



The Vrotobranchia include only a few forms, the best 

 known being the little Nut Shell (Nucula). Several 

 species of these neat little shells are abundant on our 

 sandy shores, where they often literally swarm and form 

 an important item in the menu of many fishes. The 

 animal has a deeply-toothed fringe to its foot, giving a 

 firm grip amongst grit or gravel and dragging the shell 

 about at a fair speed. 



The Filibrancbia include many valuable molluscs used 

 both for food, ornament and in one instance for clothing. 

 The Saddle Oysters (Anomia), often used for inlay work, 

 are common in most seas and are of the beautiful mother of 

 pearl consistency. The shells are invariably attached to 

 some solid object by a thick shelly plug or rivet, which 

 passes through a hole in the lower valve. The shells 

 of some of our own species are so transparent that they 

 are used for glazing windows. The plug apparently 

 corrodes surfaces to which it is attached, so that 

 the shell often lies sunk into a little pit of its own 

 making. 



The Arc Shells {Area) abound everywhere, one common 

 species, A. lacta, forms the bulk of the famous shell beach 

 at Herm in the Channel Islands. The animal anchors 

 itself by clumps of short horny threads. 



The Edible Mussel (Mytilus edulis) is typical of its group, 

 and has for long been much appreciated as an article of 

 food. Its edible virtues were not apparently recognised 

 prior to the year 1235, when a shipwrecked Irish sailor, 



