Operculinoides Hanzawa, 1935

Torres-Silva, Ana. I., Eder, Wolfgang, Hohenegger, Johann & Briguglio, Antonino, 2018, Morphometric analysis of Eocene nummulitids in western and central Cuba: taxonomy, biostratigraphy and evolutionary trends, Journal of Systematic Palaeontology 17 (7), pp. 557-595 : 582-583

Genus Operculinoides Hanzawa, 1935

Diagnosis. Planispiral, involute or partially involute in the nepionic stage, becoming evolute in the adult stage. Tests with the strongest marginal radius increase and strongest backward bend angles of the investigated individuals, producing rapidly widening coils and highly projecting later chambers. Chambers are up to 4 times as high as wide and are separated by primary operculine septa with septal undulations, which are more pronounced in loosely coiled forms. These forms with the highest values in chamber height in the adult stage have chambers up to 10 times higher than wide. The marginal cord is moderately well developed.

Characters and attributes (means and standard deviations) for Operculinoides and comparison to Nummulites and Palaeoummulites are given in Table 6 .

Occurrences. Operculinoides is common in the middle and late Eocene.

Remarks. Eames et al. (1962) included Operculinoides Hanzawa, 1935 as a synonym of Palaeonummulites based on the type species Palaeonummulites willcoxi with a tight coil producing chambers one and half times higher than long, i.e. almost square. This was followed by Haynes (1988), Robinson & Wright (1993) and Haynes et al. (2010). However, the other Operculinoides species, such as the O. floridensis group with a clear operculinid lax coiling and gradational involution, cannot be considered Palaeonummulites . It would be necessary to change the type species of Operculinoides to distinguish these forms generically. The species O. floridensis seems to be the best candidate, as has already been suggested by Butterlin (1981), because the variability of the coiling mode encompasses characteristics of Palaeonummulites , Operculinoides and Operculina .