12 INTRODUCTION 
the egg-cases of F. carica, and those having sharp edges those of 
F. canaticulata, Collar-like sandy rings contain the eggs of 
Polynices (Lunatia), which are cemented together in this shape. 
The boys of Cape Cod call them “tommy-cod houses.” Cylindri- 
eal piles of little capsules, sometimes called “ears of corn,” hold 
the eggs of Chrysodomus. The irregular masses of small hemi- 
spherical capsules are those of the common whelk (Buccinum). 
The so-called “ Devil’s pocket-books” are the egg-cases of the skate. 
MUDDY SHORES 
On muddy shores the eel-grass (Zostera marina) grows abun- 
dantly, giving an appearance of submerged meadows. It is one 
of the very few flowering plants which live in salt water. In 
summer its little green blossoms may be seen in grooves on the 
leaf-like blades. Many animals live on and among eel-grass. 
Found upon it is the delicate gasteropod mollusk Lacuna vineta, 
and its eggs in little rings; the iridescent Margarita helicina, and 
Nassa, with its bright-yellow eggs in small gelatinous masses; 
also little worms (Spirorbis) in tiny flat spiral shells, compound 
ascidians in jelly-like masses, clusters of shelly or horny poly- 
zoans, isopods, planarian worms, and so on. Scallops (Pecten) 
will be found at the base of the plants, and the common prawns 
are very numerous, swimming freely about. Mud flats and 
shores are the homes of many mollusks, especially of Massa obso- 
leta,—which is the most abundant shell of any considerable size 
from Cape Cod to the Gulf of Mexico,—and of vast numbers of the 
tiny Littorinella minuta, which serve as food for fishes and aquatic 
birds. Clams and worms of all varieties are also abundant. 
There are many varieties of mud-crabs, of which the most com- 
mon are the “fiddlers,” which honeycomb the banks and the sur- 
face of salt-marshes with their burrows. The common edible 
crab Callinectes hastatus is plentiful in bays and estuaries. The 
sluggish spider-crabs hide beneath the surface of the mud and in 
decaying weeds and eel-grass. Hermit-crabs are plentiful here 
as well as elsewhere. Panopeus is a sluggish crab found in shal- 
low water and in all sorts of hiding-places along the shore. It 
