Tropidomarga Powell 1951

“Genus Tropidomarga n.g.

Type: Tropidomarga biangulata n.sp.

The type of this new genus bears a superficial resemblance to Minolia, but the dentition shows close alliance with the boreal ‘Pupillaria’ cinerea (Couthouy). Both differ from all other Margarites-like species (of which the dentition is known to me) in the form of the basal plates of the central and laterals. The central has a large circular base, and the laterals are similar except that they are cut away on the inner side.

The type of Pupillaria (Trochus pupillus Gould, California) is tall, conical, solid, angulate at the periphery, narrowly umbilicate and sculptured with narrow spiral cords. The species cinerea (boreal) is relatively large and thin with a rounded periphery, surface sculptured with narrow, distinct, sharply raised spiral cords and has a deep narrowly open umbilicus about one-eight the major diameter of the base.

The type of Margarites (Helix margarita Montagu = Turbo helicinus Phipps) is depressed turbinate, umbilicate and smooth surfaced.

Although there is apparently a relationship between the antarctic Tropidomarga and the boreal cinerea, the latter does not conform to the genotypes of either Margarites or Pupillaria, or any other available genus.

For the antarctic species described below, I propose therefore the new generic name Tropidomarga.
This new genus has a conical shell with strongly shouldered spire whorls and a prominently biangulate body-whorl. The surface is sculptured with thin spiral lirations crossed by finer dense axial threads. At the suture the axials are thickened to form a crenulated submargining. The umbilicus is deep with straight-sided walls and has a width of about one-fifth that of the major diameter of the shell.”

(Powell, 1951: 101)

Tropidomarga is a genus of sea snails, marine gastropod mollusks in the family Trochidae, the top snails.

This genus was previously included in the family Trochidae.