- 
SHELL DREDGING. 278 

J concentric ridges., The color in young specimens is very 
= light-brown; in old ones the shell is of a brownish olive 
| color. Cardita borealis (Fig. 28) has a brownish shell with 
the ribs crenulated. Cardium pinnulatum (Fig. 33) has a 
dingy white shell, ornamented with about twenty-five ribs, 
each of which has a series of little scales. Yoldia limatula 
(Fig. 30) has a beautifully polished shell, of a light green 
color. The hinge is complicated by a number of long sharp 
teeth, so closely interlocked, that it is difficult to separate 
the valves without breaking them. Tellina tenera (Fig. 31) 
has a white iridescent shell. Nucula tenuis (Fig. 27) is 
smooth and green in color. Nucula delphinodonta (Fig. 29) 
is brownish green. All the Nuculas have the same peculiar 
hinge of numerous interlocking teeth. Crenella glandula 
(Fig. 26) has a brownish yellow shell, marked with minute 
radiating lines. Terebratulina | septentrionalis (Fig. 32), 
though apparently related to the other bivalves, is widely 
different from them and belongs to another order; the shell 
is secured to the bottom, generally on stones, by a fleshy 
peduncle which passes through a hole in the upper valve. 
Dentalium striolatum (Fig. 9) has a shell like a long curved 
tapering tube. Scalaria Grænlandica (Fig. 12) has a shell 
that looks more like a tropical species than a denizen of our 
. cold northern waters. The shell is very attractive, with its 
turreted spire banded by prominent ribs. It is related to 
the foreign species, commonly called the "Wentle trap," 
. Which formerly brought fabulous prices among shell collec- 
tors. Margarita undulata (Fig. 16) is one of our most 
i beautiful marine shells. The color of the shell when fresh 













genus, Margarita cinerea (Fig. 17), is ashy white. There 
zd Several species on the coast, a | 
is bluish white. Turritella erosa (Fig. 11) has a pale brown 
shell, and Odostomia producta (Fig. 10) has a light brown- 


AMER. NATURALIST, VOL. III. 
ell. Bela harpularia (Fig. 7) is brownish in color, 


