MOLLUSCA. * 59 
are obsolete, the ligament is external, and the shell gaping. The shell presents 
many distorted varieties, and some species excavate cavities in rocks. Some 
authors unite this family to the Lithophaga, among the Elatobranchia. 
Fam.5. Pandoride. A small family formed of the single genus Pandora, 
which has only a single branchia on each side. The shells are small, 
pearly within, the valves unequal, the ligament interior, the siphons short, 
the hinge with two diverging teeth in the right or flat valve, and two 
corresponding impressions in the left, which is convex. J. trilineata, Say 
(American Conchology, pl. 2), inhabits the American coast from Maine to 
Florida. This genus is by some placed with the Solenidx, and by others 
with the Myide. 
Fam. 6. Solenide. This family is composed of the genera Solen 
(pl. 76, figs. 45-6), Solecurtus, Glycimeris, Panopzea, and Pholadomya. 
The ligament is external, the shell gaping at both ends, and the foot is long 
and fleshy, and is passed out of the anterior extremity. The genus Solen 
lives in holes several feet deep, in which it passes up and down by means 
of its foot, and with such rapidity that it is difficult to take. Fishermen 
take them for bait by suddenly thrusting a barbed spear into their retreat, 
but if they are not struck at once they descend beyond reach. The genus 
Glycimeris is remarkable for having the body so large in proportion to the 
shell, that the latter is unable to inclose it. G. siliqua, the only species of the 
genus, as now restricted, inhabits the banks of Newfoundland, and the shell 
is usually got from the stomachs of cod-fish. Panopeea is a genus including 
species mostly of a large size, few in number, and occurring recent and fossil. 
P. arctica inhabits the banks of Newfoundland, and about eight fossil species 
have been named from the tertiary formations of the United States. 
Fam. %. Pholadide. This family contains various genera, which live in 
perforations which they make in rocks, wood, or clay, each being a prisoner 
for life in a cell of its own construction. In Pholas (pl. 76, jigs. 49, 50) 
the shell is widely gaping, and provided with accessory pieces at the hinge 
( fig. 49), and the foot is shaped like a sucker. Pholas dactylus (fig. 50) 
is used as food. A few fossil species are found in the tertiary formations 
of Europe and America. The genus Teredo is placed by some authors in 
the next family, Zudzcola, on account of its form ; but Deshayes thinks the 
characters of the animal require that it should be placed_here. Zeredo 
navalis (pl. 75, fig. 67), which is so destructive to timber and shipping 
when not protected, appears as a long, sinuous, calcareous tube, lining 
perforations in wood, and if one of these be followed to its lower end, the 
valves of the shell will be found. The shell is thick, and so short as to be 
annular, having a single adductor muscle, and the posterior extremity of the 
tube is open. According to Laurent, when the young Teredo escapes from 
the egg, it swims about by means of vibrille. At first the body is inclosed 
in the shell proper, and the little animal can move about with the aid of a 
long linguiform foot. After spending about twenty-four hours in swimming 
and moving about upon submarine objects, it attaches itself to wood, 
making a depression in which it locates itself, and excretes a mucous mass 
which covers it, but allowing a passage for the siphons. The young animal 
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