4 AMPULLARIA. 
AMPHIBULI'MA. Lam. Svccrnea Patula, Auct. fig. 266. 
AMPHIDESMA. Lam. (from Apdi, amphi, both, Acecpos, desmos, 
ligament.) Fam. Mactracea, Lam. Descr. Equivalve, oval orround- 
ed, sub-equilaternal, sometimes rather gaping at the sides, with a 
slight posterior fold; hinge with one or two cardinal teeth in each 
valve, and two elongated lateral teeth, distinct in one valve, 
nearly obselete in the other; ligament short, separated from the 
cartilage, which is elongated and couched obliquely in an exca- 
vation of the hinge. Obs. In most bivalve shells the cartilage 
and ligament are united in one mass, or placed close to each 
other; the contrary in this case gives rise to the name, which 
signifies, double ligament. This circumstance distinguishes the 
genus Amphidesma from Tellina, which in other respects it 
greatly resembles. From Lutraria it may be known by its distinct 
lateral teeth, and also by its valves being nearly close all round, 
while the Lutrarize gape anteriorly. The species do not appear 
to be numerous, no fossil species are known. <A. Reticulatum, 
fig. 85. 
AMPHISTEGINA. D’Orb. A genus of microscopic Foramini- 
fera. 
AMPLEX'US. Sow. A. Corrailoides, fig. 463. A singularly 
formed fossil, described as nearly cylindrical, divided into cham- 
bers by numerous transverse septa, which embrace each other 
with reflected margins. It occursin the Dublin limestone, and 
resembles a coral or madrepore. 
AMPULLARTA. Lam. (Ampulla, a rounded vessel.) Fam. 
“ Peristomiens,”’ Lam. Ellipsostomata Bl. Descr. Spiral, glo- 
bular, sometimes discoidal, generally umbilicated, covered witha 
horny epidermis; spire short, whorls rapidly enlarging ; aperture 
elliptical, deciduous, rounded anteriorly; peristome nearly or 
quite entire, thickened, and slightly reflected; operculum tes- 
taceous, annular, with a subcentral nucleus. Obs. These 
freshwater shells of which a few fossil species occur, are 
easily distinguished from other genera, by their obvious cha- 
racters, particularly by the thick, horny, greenish brown epi- 
dermis which covers them, and the rotundity of their form. 
One species the A. Cornu-arietis, which forms the type of La- 
marck’s genus Planorbis, requires notice, on account of its 
flatness, but may be known by the aperture, which in the Am- 
pullaria is longer than wide, and in Planorbis, the contrary. La- 
nistes, Montf. is described from a reversed Ampullaria. The 
Ampullaria is vulgarly called the Idol Shell,and is said to be held 
in great veneration by the S. American savages. The animal 
has a large bag, opening beneath, placed on the side of the respi- 
rator cavity. It is supposed that the animal has the power of 
filling this bag with water, and that it is thus enabled to live a 
long time out of water. They have been brought as far as 
from Egypt to Paris, alive, packed in sawdust. Ex. Fig. 318. 
