Genus Munditia Finlay.
Type (o.d.) : Liotina tryphenensis Powell.
Munditia proavita n.sp. (Figs. 49, 51).
Shell very small, flat above, widely umbilicate below. Whorls 3, rapidly increasing. Protoconch tiny, of one smooth volution. Fine, close microscopic radial threads present between heavier axials, but probably originally universal (as in tryphenensis), the surface being somewhat rubbed. Axial corrugations present on all adult whorls, becoming prominent on last volution, which bears 17 of them. These corrugations are very weak on upper surface and on base, but are strongly developed over the peripheral convexity. There are 4 spiral keels, one within umbilical depression, one on middle of base, a third at the periphery, and a fourth above periphery at edge of upper flat surface of shell. There is also a low swelling a little
distant from suture, which is channelled. Axial serrations extend from preceding whorl into the sutural channel. There are teeth-like axial crenulations on umbilical carina, projecting into umbilicus. Aperture circular, its rim not appreciably thickened. Umbilicus deep, wide, perspective.
Diameters—greatest, 2.1 mm. least, 1.7 mm. (holotype).
Type in writer's collection.
Tryphenensis is the nearest relative of this species, which can be distinguished by its strong peripheral keel, development of axials around whole circuit of whorl, smaller protoconch and less rapidly enlarging whorls. M. serrata (Suter) has axial serrations developed around entire whorl, but does not agree in the number of keels; and, further, axial corrugations are not present over periphery and on base.
This is the first fossil species of the genus to be recorded.