J13 
EAST. ZOOL, GAL.] NATURAL HISTORY. 
produced, very thick and black, and the syphons are 
united. 
Ctenoconclia , which has many characters in common with 
the Solens, has the teeth like Nucula, but it has an ex¬ 
ternal cartilage. 
The family of Anatinidce have a broad compressed foot; 
the edges of the mantle-lobes are thickened, and the sy¬ 
phons are elongate and more or less united ; the shells 
are oblong, thick, and brittle, covered w r ith a granular or 
spinular periostraca ; the hinge is obscurely toothed ; the 
cartilages are internal, placed in a pit in each valve, and 
furnished with a peculiar shelly hinge-piece, which is either 
placed before it or sometimes so as to cover the whole 
of its surface. In most of the genera the shell is regular 
and free. In Auriscalpium , Periploma, Coclilodesma and 
Hemicyclostoma , the cartilages are in a pit on a projecting 
spoon-shaped process, and the hinge-piece is small. In 
Thracia the cartilage is on a callosity of the hinge margin. 
In the Lyonsice and Myadorce , the cartilage pit is sunk 
into the hinge margin of each valve, and covered by a 
large flat hinge-piece ; the shell of the former is thin and 
of the latter thick, with very unequal valves, the left one 
being flat. Chamostrea and Myochama differ from the 
rest in the shell being irregular and attached by the outer 
surface of one of the valves. 
The family of Myadce are very like the former, but 
the cartilage is placed on a spoon-shaped cavity in one of 
the valves, fitting into a pit in the surface of the other; 
there is no hinge piece, and the hinge is toothless ; the 
syphons are long and the lips small. 
The family of Corfoilidce differ from the former in 
having small tubes and very large lips ; in the right valve 
being the largest; and in being provided with a large 
tooth in each valve in front of the cartilage pit. 
The family of Pandoridce have very unequal valves and 
pearly shells, with two diverging teeth in each valve, near 
the cartilage pit. They have short tubes, like the Corbu - 
lidcE, but the foot is small, the gills on each side are 
united into one, and it is the left valve that is the most 
concave. 
The family of Soleiiomyadce are very peculiar for being 
covered with a very hard cartilaginous periostraca, which 
