GALLERY.,] NATURAL HISTORY. 79 
are united together behind, and pierced with a hole; the foot is com¬ 
pressed, rhombic, rounded at each end, produced in front, and the 
hinder part of the lower edge is doubled and fringed, like the Area ; when 
distended it is cylindrical, with a flat linear disk. 
The family of Saxicavid^: have the mantle lobes united together, 
leaving only a small hole in front for the passage of the tongue-like 
foot, which is furnished with a tuft of byssus at its base, and the mantle 
is produced behind into two large united syphons; the shells are equi- 
valve, rugose, wedge-shaped, and with a moderate syphonal inflection 
and a muscular scar near its lower edge ; they live in holes in stones or 
attached to stones by their byssus. The Saxicava have a toothless hinge, 
and the Hiatella have two indistinct teeth in each valve, but the latter 
have been considered as only the young of the former. 
The family of Lasiam: have oblong equivalve shells, with two 
cardinal teeth in the left valve and one in the right, in front of the sub¬ 
marginal internal cartilage; they have no syphonal inflection, the mantle 
lobes are separate below, the foot elongate, very exsertile, with a slight 
groove along the low T er edge, sometimes furnished with a byssus ; they 
have a single very short syphon ; they are very like Cyclades , but are 
marine, living in cracks of rocks, or between the roots of fuci, and 
float on the surface of the water and crawl up the edge of a fucus like 
a Gasteropode; they are viviparous. The Lasea are ovate convex, 
the Kellia are suborbicular swollen, and the Lepton are orbicular and 
much compressed, like a fish scale. 
II. In the more aberrant orders the mantle is not provided with any 
distinct syphons, but the lobes are either free behind or united and 
pierced with one or two holes for the passage of the water. 
In the two following orders the animals have oblpng elongated shells, 
like the preceding, and two distinct adductor muscles, leaving more or 
less distinct scars on the inner surface of the shell, which shews the 
places the muscles have occupied when the animal was alive. 
The Goniopoda have a more or less compressed angular foot; the 
mantle without any syphons. The lobes are united so variously and so 
differently in genera that are evidently very nearly allied, that we are 
led to believe that in this order it must afford a veiy secondary charac¬ 
ter. They may, however, until more is known of the animals, be 
arranged in the following families. 
In some the shells are adherent to other bodies by the outer surface 
of their valves. 
In the family Chamidce , the mantle lobes are united, leaving only a 
small hole for the passage of the small elongate oblong foot. The 
. shells are porcellaneous, and the animals attach themselves to rocks, 
coral, and shells on the sea-shore. The Chama are attached by the 
outer surface, and the Arcinella only by the top of the valve, and are 
regularly cordate, while the Chama are distorted. 
The family Etheriada are fluviatile, being attached to stones and 
shells in the African rivers. Their mantle-lobes are free, with a large 
quadrate foot, like the Uniones, and the shell is pearly and blistered in¬ 
ternally, and covered with a green periostraca, which is often eroded. 
The genus Mulleria appears to have been established on a distorted 
Etheria . 
