Genus Monophyllum Fomichev, 1953.

Type species: Monophyllum sokolovi Fomichev, 1953.

M. sokolovi Fomichev, 1953;? 1953 M. parvum Fomichev 1953; M. cassum Fedorowski, 1987.

Diagnosis: Non-dissepimented, small solitary corals, with major septa radially arranged, may withdraw a little from corallite axis in maturity; cardinal septum shortened from early maturity; counter septum permanently elongated to corallite axis; alar septa slightly elongated at least in some portion of growth; minor septa underdeveloped (after Fedorowski, 1987a, p. 67).

Remarks: In contrast to Hill (1956, 1981), de Groot (1963) and Weyer (1975) who listed Monophyllum Fomichev, 1953 as a synonym of Rotiphyllum Hudson, 1942, Fedorowski (1987a) considered it as a separate genus. This view was followed by Kossovaya (1996, 2001), Ogar (2012) and Wang et al. (2017). Fedorowski (1987a) mentioned the following differences to Rotiphyllum and further similar antiphyllinid genera (see also Table 1):

• Monophyllum differs from Rotiphyllum by: (1) the strongly and permanently elongated counter septum reaching the corallite axis, even on the calice floor, where it may form an incipient columella, (2) shortening of the cardinal septum not only on the calice wall as in Rotiphyllum, but also on the calice floor, (3) the triangular shape of at least peripheral parts of the cardinal fossula at maturity.

• Monophyllum differs from Bradyphyllum by the permanently elongated counter septum that reaches the corallite axis and tends to form an incipient columella. Although Monophyllum develops a tendency to form an axial area free of septa, like most of the genera included in Antiphyllinae (Illina, 1970), its counter septum remains elongated, which is not the case in Bradyphyllum.

• Monophyllum differs from Actinophrentis Fomichev, 1953 by (1) the radial arrangement of septa in the mature portions of Monophyllum vs. the pinnate arrangement of the major septa lasting up to the calice floor in Actinophrentis and (2) the lacking tendency of Actinophrentis to form a free axial area.

Species described by Fomichev (1953) to be “ Stereolasma ” might belong to Rotiphyllum (in toto, see Hill, 1956; de Groot, 1963), to Monophyllum and/or other Antiphyllinidae (Fedorowski, 1987a, p. 36, 68).

Geographic and stratigraphic range: Monophyllum is a long ranging but relatively rare genus. It is known from the Bashkirian of the Donets Basin (Fomichev, 1953; Kossovaya, 1986, Fig. 7; Fedorowski, 2022, Fig. 2: M. sokolovi Fomichev, 1953, M. parvum Fomichev, 1953), the Moscovian of the same region (Fomichev, 1953: original designation of the type species M. sokolovi; Kossovaya, 1986, Fig. 7; Ogar, 2012) and the Moscovian of Novaya Zemlya (fide Fedorowski, 1981 and Wang et al., 2022). It is also known from the Pennsylvanian–Permian transition and the Wolfcampian (Asselian–middle Artinskian) of southwest Texas (Fedorowski, 1987a: M. cassum Fedorowski, 1987). Kossovaya et al., (2001, Fig. 6) figured? Monophyllum sp. from the late Artinskian of the Urals and/or northern Timan Ridge (not further specified). Herein, we report the genus from the Kasimovian west of the Gulf of Suez, Egypt.