424 MARINE INVERTEBRATES 
junctures are so slight that they break readily when a specimen 
of a gill is handled, leaving the filaments free. The presence of a 
byssal gland in the foot, and often-a well-developed byssus, is 
another characteristic of this order. 
FAMILY ANOMIIDE 
GENUS Anomia 
This is a family of peculiar and highly specialized forms. 
Anomia has an irregularly rounded shell, with one convex and 
one flat or concave valve. There is no regular hinge or well- 
defined hinge-margin, but a raised fossette, or cartilage plate, occu- 
pies a position at the top of the valves. In the flat valve there 
is a large oblong hole just under the apex, through which projects a 
calcified byssus, by means of which the animal secures itself to 
oysters, dead shells, stones, or any solid object. The anomias, which 
have become stationary in habit, have practically Yost their foot. 
The gills are very large and curved, while all the organs seem to 
be abnormally placed on account of the huge byssus and byssal 
muscle. For the byssus to pass, as it does, through a specially 
prepared hole in one of the valves is an extraordinary departure 
from the conventional types of byssiferous species. The heart is 
not traversed by the intestine. Altogether, then, Anomia is a very 
curious genus. 
A. simplex. The commoner large form of New England. It varies 
from one to three inches in diameter, is exceedingly irregular in shape, 
and its surface is var- 
iously undulated and 
plaited in accordance with 
the surface of the ob- 
ject to which it is at- 
tached. Thousands of 
these valves, disjointed 
and separated, are cast 
upon the beachesall along 
our Atlantic coast. They 
are light green to sal- 
mon- or copper-color, 
generally fragile and 
sealy, and have a _pecu- 
liarly dulled (as though 
Anomia simplex, side view. Anomia simplex, from below. greased) nacre. 
