Basal and mitral gates of the shell of about equal size, roundish.
Eight gates (two mitral, two basal, and four superior) simple; four inferior gates fenestrated by arachnoidal irregular threads.
mitral and basal gates of equal size, the lower and upper halves of the two crossed lateral rings being nearly equal.
mitral gates smaller than the basal gates; upper halves of the two lateral meridional rings smaller than the lower halves.
Basal ring larger than the mitral ring, with numerous irregular short spines but without descending feet.
Basal ring of about the same size as the mitral ring, with three large and stout divergent feet (two lateral and one caudal).
Lattice of the mitral ring hemispherical, with six roundish pores, surrounding a central apical horn.
mitral and basal rings of equal size, equilateral triangular, both connected at the corners by three vertical equal columell.
The latter are connected with the former by eight divergent, curved columell, as long as the diameter of the mitral ring.
mitral and basal ring hexagonal, the latter twice as broad as the former, each with a simple small spine on the six corners.
mitral mi·tral (mī'trəl)
Relating to a mitral valve.
Shaped like a bishop's miter. Used of a structure resembling the shape of a headband or turban.