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Odontochitina rhakodes
Odontochitina rhakodes Bint, 1986
Holotype: Bint, 1986, pl.1, figs.9-10
Locus typicus: Western Interior, U.S.A.
Stratum typicum: Middle Albian-Early Cenomanian
Original description: Bint, 1986, p.140, 142
Large cysts with ceratioid outline and three well developed, blunt horns: apical, antapical, and right lateral. Each horn terminates with an irregular, perforate margin. Right lateral horn extends at nearly right angles to the endocyst margin for a short distance then recurves posteriorly, with a cingular notch at the point of recurvature. Cornucavate; endocyst subspherical or produced slightly into horn bases, with circular equatorial section. Periphragm separated from endophragm at horns, but hypocystal pericoels may be enlarged beyond horn bases. The antapical pericoel has an elongate extension up the left ventral surface as far as the cingulum.
Endophragm smooth; periphragm smooth, scabrate, or sparsely granulate, but becoming increasingly perforate toward ends of horns. At horn extremities periphragm is strongly perforate and ragged, having the appearance of a broken edge. Number of perforations in distal part of horn usually greater than 20, and often much greater. Perforations typically subcircular and usually 1-3 µm in diameter but some may be quite large, up to about 7 µm across. Larger perforations may be elongate about parallel to the horn axis. Archeopyle apical, type (tA), operculum free. Archeopyle suture weakly angular, sulcal notch offset slightly to the left. Paratabulation not expressed. Cingulum indicated by faint transverse lines to low parasutural ridges, but always absent on right side of ventral surface; also indicated by a distinct notch in the right lateral horn. Left edge of sulcus probably delimited by ventral extension of antapical cavation.
Size. Endocyst diameter 47(54)68 µm; length of complete specimen 130(144)163 µm, 6 measurements; length with operculum detached 78(94)111 µm, 14 measurements; length of lateral horn 25(33)43 µm and antapical horn 25(40)57 µm; length of apical horn 36(43)50 µm, 6 measurements; 20 specimens measured. Length of three detached opercula 65-88 µm, apical horn 43-67 µm.
Affinities:
Bint, 1986, p.142: Odontochitina rhakodes differs from O. ancala in having shorter, blunted horns which are distally ragged and perforate. On O. ancala the horns have an additional pointed portion beyond the site of localized perforations. Rare specimens of O. rhakodes have part of this distal portion of the horn present, but the pointed tip is still missing. Thus, morphologically, O. rhakodes can be viewed as having developed from O. ancala by removal of the distal portions of the horns beyond the localized perforations. Xenascus plotei is similar to O. rhakodes but differs in that the periphragm bears spines.
Samples examined in this study may contain O. rhakodes to the exclusion of O. ancala or vice versa, and the former species ranges into the Cenomanian in the Western Interior whereas the latter does not. These data seem to support the separation of the two forms at the specific level rather than at the subspecific level.
Holotype: Bint, 1986, pl.1, figs.9-10
Locus typicus: Western Interior, U.S.A.
Stratum typicum: Middle Albian-Early Cenomanian
Original description: Bint, 1986, p.140, 142
Large cysts with ceratioid outline and three well developed, blunt horns: apical, antapical, and right lateral. Each horn terminates with an irregular, perforate margin. Right lateral horn extends at nearly right angles to the endocyst margin for a short distance then recurves posteriorly, with a cingular notch at the point of recurvature. Cornucavate; endocyst subspherical or produced slightly into horn bases, with circular equatorial section. Periphragm separated from endophragm at horns, but hypocystal pericoels may be enlarged beyond horn bases. The antapical pericoel has an elongate extension up the left ventral surface as far as the cingulum.
Endophragm smooth; periphragm smooth, scabrate, or sparsely granulate, but becoming increasingly perforate toward ends of horns. At horn extremities periphragm is strongly perforate and ragged, having the appearance of a broken edge. Number of perforations in distal part of horn usually greater than 20, and often much greater. Perforations typically subcircular and usually 1-3 µm in diameter but some may be quite large, up to about 7 µm across. Larger perforations may be elongate about parallel to the horn axis. Archeopyle apical, type (tA), operculum free. Archeopyle suture weakly angular, sulcal notch offset slightly to the left. Paratabulation not expressed. Cingulum indicated by faint transverse lines to low parasutural ridges, but always absent on right side of ventral surface; also indicated by a distinct notch in the right lateral horn. Left edge of sulcus probably delimited by ventral extension of antapical cavation.
Size. Endocyst diameter 47(54)68 µm; length of complete specimen 130(144)163 µm, 6 measurements; length with operculum detached 78(94)111 µm, 14 measurements; length of lateral horn 25(33)43 µm and antapical horn 25(40)57 µm; length of apical horn 36(43)50 µm, 6 measurements; 20 specimens measured. Length of three detached opercula 65-88 µm, apical horn 43-67 µm.
Affinities:
Bint, 1986, p.142: Odontochitina rhakodes differs from O. ancala in having shorter, blunted horns which are distally ragged and perforate. On O. ancala the horns have an additional pointed portion beyond the site of localized perforations. Rare specimens of O. rhakodes have part of this distal portion of the horn present, but the pointed tip is still missing. Thus, morphologically, O. rhakodes can be viewed as having developed from O. ancala by removal of the distal portions of the horns beyond the localized perforations. Xenascus plotei is similar to O. rhakodes but differs in that the periphragm bears spines.
Samples examined in this study may contain O. rhakodes to the exclusion of O. ancala or vice versa, and the former species ranges into the Cenomanian in the Western Interior whereas the latter does not. These data seem to support the separation of the two forms at the specific level rather than at the subspecific level.