360 MARINE INVERTEBRATES 
long and slender, with short peduncles for the eyes; the opercu- 
lum is corneous, with a central nucleus. The animals are herbiv- 
orous, feeding upon alge. The trochids are essentially tropical 
shells, and the most of the genera which are comprised in the 
family are only to be encountered in the warm waters of the 
Pacific and Indian oceans. Some forms are very beautiful, and 
frequently are used as mantel ornaments, and the shells of one 
little species, which is opalescent in its coloring, are still exten- 
sively gathered in the East Indies, to be polished and strung like 
pearls in necklaces. 
Genus Margarita 
On the Atlantic coast north of Cape Cod the trochids are rep- 
resented by the genus Margarita, with five or six species. The 
shells are small, thin, and globosely depressed, with smooth or 
transversely striated whorls. The aperture is nearly circular, 
with a simple lip. 
M. cinerea. This species has several prominent revolving ridges 
upon the upper side of the whorls, with finer ones on the base. Very 
fine growth-lines cover the entire shell. It ranges all along 
the coast north of Cape Cod, but is not usually found between 
tides. The writer has dredged many specimens in shallow 
water at Eastport and Bar Harbor. 
M. helicina. A thinner and more globose species than the 
last, with a translucent, shining, smooth surface of a yellow- 
ish or olive color. MM. helicina is very fond of the leaves of 
Laminaria, and is often found clinging to them when 
storms have torn these great alge from the bottom and 
cast them upon the shore. At Bar Harbor they are com- 
mon upon the eel-grass in Rodicks Weir. This species can 
generally be distinguished by its iridescent, metallic luster. 
M. undulata. A commoner species, perhaps, than 
either of the preceding, sometimes found on the rocks of sheltered 
coves at exceptionally low tides. Judging from the number 
often to be found in the stomachs of fishes, they must be con- 
sidered excellent food by the cod and its allied species which 
thrive along the Maine coast. No doubt millions of M. undulata 
are yearly destroyed in this way. The shell is depressed, 
with four rounded whorls, a flattish base, and a large umbilical 
opening. In color it varies from rose-red to brown. The surface 1s deco- 
rated with numerous revolving raised lines placed at uniform distances. 
Just below the suture the body-whorl is somewhat undulated with short 
folds. Height three tenths of an inch, base four tenths of an inch. 
Margarita 
cinerea, 
Margarita helicina, 
Margarita 
undulata, 
