BIVALVE MOLLUSCA. 333 
have the tube covered with a glutinated sand, mixed with small frag- 
ments of shells of diverse colours. We know nothing of their habits, 
and their singular forms have left naturalists in doubt as to the place 
which should be assigned to them. It is only after having recognised 
the existence of two valves, which were detected with great difficulty just 
under the disc, and forming part of the sheath in which the animal is 
encased, that it has been decided to range them with the Gastroche- 
nidz, and with the shells presenting an arrangement analogous and 
equally singular. These molluscs are, as M. Chenu says, little known, 
rare, and hence much sought for by collectors. They are exclusively 
exotic, the most common species being from Java. It is imported 
into Europe by the Dutch. A third family, the Anatinidze, includes 
such genera as Myochama, Pandora, Lyonsia, Myacites, Pholadomya, 
Thracia, and Anatina, genera which were more important in the 
former than in the present seas ; some, in fact, being wholly extinct, 
or represented, as in Pholadomya, by but one living species. A fourth 
family, the Myacidze, including Glycimeris, which is found only in 
America; Panopsea, now for the most part extinct, Thetis, Nezra, 
Corbula, and Mya. 
A fifth family, Solenidz, contains the Solens, which under the 
name of “razor-fish” are so abundant on the sandy shores of all parts 
of the globe. These molluscs live with their shells buried verticaliy 
in the sand, a short distance from the shore; the hole which they 
have hollowed, and which they never quit, sometimes attains as much 
as two yards in depth; by means of their foot, which is large, conical, 
swollen in the middle, and pointed at its extremity, they raise them- 
selves with great agility to the entrance of their burrow. They 
bury themselves rapidly, and disappear on the slightest approach of 
danger. 
When the sea retires, the presence of the Solen is indicated by a 
small orifice in the sand, whence escape at intervals bubbles of air. 
‘In order to attract them to the surface, the fishermen throw into the 
hole a pinch of salt; immediately the sand becomes stirred, and the 
animal presents itself just above the point of its shell. It must be 
seized at once, for it disappears again very quickly, and no renewed 
efforts will bring it to the surface a second time. Its retreat is 
commonly cut short by a knife being passed below it ; for it burrows 
into the ground with such velocity that it is difficult to capture it with 
the hands alone. 
This shell has by some been compared to a knife-handle; by 
others to. a razor, which has become its popular name. It is a thin, 
transparent, long, and slender equivalved bivalve, with parallel edges, 
