458 MARINE INVERTEBRATES 
cutting off his retreat. So tenaciously will they cling to the sand 
by expanding the muscular foot that the shell may be pulled en- 
tirely off the body before they will let go. 
Genus Einsis 
E. directus (Solen ensis, Ensis americanus). 
The common species upon the New England and 
Jersey coasts. The footislong, and protrudes from 
one end of the long shell; it is also very strong, 
and capable of change at will into almost any form, 
from a pointed bulb to a flat disk. The siphons, 
which project from the opposite end of the shell, 
are short and are not united. The gills are long. 
The juxtaposition of these organs is at first con- 
fusing, because the greatly elongated form of the 
shell and the habits of the animal in burrowing 
vertically into the sand have caused the foot to be 
pushed farther away from the posterior portion of 
the shell and to protrude in a direction just opposite 
to the siphons. The shells are bent or slightly 
curved; they gape at both ends; and they are 
fitted with very small interlocking teeth at the up- 
per corner of the posterior end. The color is white, 
but a yellowish or greenish glossy epidermis covers 
the entire test. Length about six inches. The 
manner in which the animal makes its rapid de- 
scent into the sand is very interesting. First ex- 
tending the foot lengthwise into a point, it plunges 
it into the sand; then, by forcing water into the 
organ it expands it, thus pushing away the sand on 
all sides; and still further expanding the foot at the 
end into a disk, it secures an anchorage which en- 
ables it to draw down its shell. By quick repe- 
tition of this process Ensis can get out of sight in 
a remarkably sudden manner. 
Genus Solen 
S. viridis. A smaller species, about two inches 
in length, and with a nearly straight light-green 
a” Itis often abundant from New Jersey south- 
ward. 
Ensis directus. S. sicarius. The common Californian species of 
. Northern range. It is only about two inches long, 
and is rounded anteriorly, but is chopped off squarely behind. It is 
slightly curved and white, and has a glossy brown epidermis. 
S. rosaceus. Another species of Southern range, very similar in form 
to the last, but straighter and rosy-white in color. The epidermis is 
glossy brown. Length two inches. 
