174 ^^^ell Life 



localities for this species, and there it may be found 

 burrowing slightly in the sand at low water. It has 

 a trick of squirting water from its siphons when 

 alarmed, like the Piddocks. There is a variety ohtusa 

 found in deeper water (from 7 to 50 fathoms), and 

 the difference in habitat has produced a corresponding 

 difference in the shape of the shell. The normal 

 shallow-water form has to burrow beneath the sur- 

 face in order to escape the effects of the surf, and 

 consequently its shell is extended into a blunt beak 

 behind to protect the lengthened siphons. In deeper 

 water there is no fear of such disturbance, and there 

 is no need for burrowing so deeply ; therefore the 

 siphons are shorter and the shell less drawn out 

 behind. This is another object lesson in Nature's 

 manufacture of species. The Norwegian Lyonsia 

 (Lyonsia norvegica) is in general shape much like 

 Pandora, but the upper margin is more horizontal, 

 and there is less difference in the size of the two 

 valves. It is very thin, but opaque and yellowish ; 

 the surface made dull by fine radiating lines crossed 

 by the lines of growth. The pale brown epidermis 

 is gelatinous, and has the property of attaching grains 

 of sand and fragments of shell to itself. The golden 

 cartilaofe is contained in grooves as in Pandora, and 

 the hinge-plates are similarly ribbed and furrowed ; 

 but the cartilage is covered by a plate, called an 

 ossicle, that is not attached to the shell but formed 

 separately. The interior of the shell is iridescent. 

 The animal is white with a yellowish tinge. The 

 forepart of the mantle has a slight fringe of a few 

 projecting points. The siphons are short, fringed at 

 their orifices, and havinof a few filaments round the 



