Remarks: In its mature growth stage, Macromargarya n.
gen. basically resembles several species of Margarya, in
particular M. spinicostata Li, 1987 from the Oligocene of
Yunnan, which is cone-shaped and ornamented with a single
central carina carrying relatively widely spaced, long,
open spines. Another species of similar shape, which is also
ornamented with a central carina carrying open spines, is
the extant Acanthotropis partelloi (Bartsch, 1910), which is
endemic to Lake Lanao (Mindanao, Philippines). However,
Macromargarya differs from any other viviparid gastropod
genus in its strange, unique ontogeny, passing from an early,
low-trochospiral growth stage to a high-conical adult shell
with a marked shift of the coiling axis.