M. vulsellatus. The tweezer Malleus.
Species slightly auricled.
M. normalis. The square Malleus.
Species without earlike appendages.
4. Avicula. Thirteen species.
Remarkable for the form of its shell, which resembles, when partially expanded, a bird flying.
Shell foliaceous or not, thin and very fragile, always pearly, sub-equivalve; form sub-regular, but rather variable; summit anterior; valves oblique, the left one with a little notch, through which the byssus passes; sometimes unequally and obliquely auricled; hinge linear, toothless, or with two small rudimentary teeth; ligament more or less exterior, placed in a narrow groove, sometimes enlarged towards the summit; one very large posterior muscular impression; and one very small anterior.
Avicula macroptera.
A. lotorium.
A. semi-sagitta.