X1V CLASSIFICATION. 
9. Donax: Hinge with a lateral tooth, generally remote, not 
10. 
11. 
22. 
let into the opposite valve. 
Venus: Hinge with generally three approximate divari- 
cated teeth. 
Sponpyius: Hinge with two teeth, separated by a small 
hollow. 
. Cuama: Hinge on one side, with an oblique obtuse 
tooth inserted info a corresponding cavity. 
. Arca: Hinge with numerous penetrating teeth. 
. OstrREA: Hinge without teeth, but an ovate hollow. 
. Anomia: Hinge without teeth, but generally a linear de- 
pression on the rim, the beak of one valve curved over 
the hinge. 
Mytitus: Hinge without teeth, witha subulate depres- 
sion. 
. Pinna: Hinge without teeth, valves united at one end, 
and open at the other. 
ill. UNIVALVES. 
1. Witha regular Spire. 
. Argonaura: Shell with one cell, spiral, involute. 
. Nautitus: Shell with many chambers, communicating 
by a tube. 
. Conus: Aperture effuse, longitudinal, without teeth. 
Cypre#a: Aperture effuse, linear, longitudinal, toothed 
oneach side. 
Buxua: Aperture rather contracted, and placed obliquely. 
. VoLuta: Aperture effuse, the pillar plaited. 
. Buccrnum: Aperture with a small canal leaning to the 
right. 
. Stromeus: Aperture with a smal} canal leaning to the 
left. 
. Murex: Aperture with a small straight canal. 
