132 SEA-SHORE LIFE 
esting relative of the mussel family. It is common in shallow 
water along the sandy shores of the West Indies and Florida, and 
extends as far north as the North Carolina coast. Each valve of 
the shell is fan-shaped, with a sharp-pointed apex and a wide, 
sharp-edged margin. It attaches itself by means of a strong 
byssus-thread to a rock beneath the sand, and the broad edge of 
the shell projects above the surface of the ground. ‘The valves of 
the shell open and shut rythmically, thus creating a current of 
water over the gills and drawing minute organisms into the ever 
open mouth. The razor shells, owing to their great abundance, 
and sharp edges, render wading with bare feet all but impossible 
on parts of the Florida coast. 
THE FRESH-WATER MUSSELS. 
There are fully 600 species of fresh-water mussels in the 
streams of the United States, and more than three-quarters of them 
live in the Mississippi and its tributaries. The shells are usually 
elongate and covered with a thick outer skin. The two valves of 
the shell are similar each to each, and there is a well developed 
foot, by means of which the animal ploughs along through the mud 
making a deep furrow with only about one-half of the posterior end 
of the shell projecting. There are two large openings in the man- 
tle at the posterior end of the shell, and these openings are usually 
beautifully fringed. The one nearest the hinge side is the anal 
aperture while the other serves to admit water and minute organisms 
into the gill chambers. Although usually dull brown or greenish 
in color on the outside, the inside of the shells are beautiful, some 
being purple-black, others silvery white, golden copper color, salmon- 
pink or yellow. On this account they are highly prized for the 
manufacture of buttons, and this industry on the Mississippi alone 
is worth $40,000 annually. Valuable pearls are also obtained from 
these mussels. 
The eggs of the fresh-water mussels are carried in pouches 
between the layers of the outer gills, and there they remain until 
they have developed a bivalve shell, the Lps of which are armed 
with sharp, hook-like spines. The little mussel is then cast out and 
drops to the bottom where it comes to rest with the open valves of 
its shell upwards, and then it thrusts out a long, glutinous, thread 
