140 THE HALL OF SHELLS. 
some were fine as silk, in others stiff and 
horny. These were attached by strong mus- 
cles to themselves, and thence to rock, reef, 
or wreck, as pleased the little spmner. 
“These threads are spun by the foot of the 
little animal, and are so stout as to withstand _ 
the shock of the incoming seas. When wish- 
ing temporary anchorage, or fearing the stress 
of waves, it has only to throw out its byssus 
cable and rest secure. Sometimes this little 
bark with its silken moorings is freighted with 
pearls,” said he, pomting to a mussel; “the 
pearls of these shells, however, are generally 
of an inferior order. 
“The Pinna, or fan mussel, is a byssus 
spinner, having valves two feet long; and the 
beautiful silk of its byssus has been used in 
spinning rich and costly fabrics. 
“We find among these not only the spin- 
ners of silk, but borers of wood and stone, and 
hence some of them have received the name 
‘wood eaters’ or ‘stone eaters.’ 
“ How these little creatures are able to bore 
into hard substances has long been a question 
of wonder and speculation. The serrated or 
filelike edges of some shells might seem to 
account for it in a measure; the abrading foot 
with its strong muscles, sometimes assisted by 
