EAMP-SHELES AND THEIR: ALLIES 21 
Nucula ténuis, var. lurida, Gld., the Thin Nut- 
shell, is the common species found in moderate 
depths about Alaska, and in deeper water farther 
south. It has been known as N. expansa, KRve. 
Nucula carlotténsis, Dall, the Charlotte Nut- 
shell, is a small species, only 6 mm. long, dredged 
from deep water off Queen Charlotte’s Islands by 
the U. S. Steamer ‘‘ Albatross.’’ It has been con- 
founded with N. exigua, Sby., which is a Panama 
shell, smaller, more inflated, and with less con- 
spicuous sculpture. 
The shells belonging to the Family of the Lédi- 
de are grouped under two genera, Léda and 
Yoldia. Specimens are not common, most of the 
species living in the sea where the water is deep 
and cold. A good many species have been found 
off various parts of the coast. The shells are 
mostly small, and are rounded at one end, while 
the other end is more or less prolonged into a 
horn or hook. Internally, there are many small, 
ecomb-like hinge-teeth, extending away from the 
center on either side. Externally the shells have 
many concentric markings, and when fresh are 
covered with a smooth, almost transparent epider- 
mis. Only a few species will be described here, 
while others will be mentioned in the List, near the 
end of the book. 
Figure 9 represents Léda ha- 
mata, the Hooked Leda, though 
the picture is nearly three times 
—— as long as the real shell, as is in- 
Bie a dicated by the fraction, }. The 
