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Didymocyrtis avita (Riedel , 1953)

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Panartus avitus Riedel, n. sp. Plate 84, figure 7

Four chambers of the cortical shell of similar general form, kidney-shaped (as in Panartus tetrathalamus Haeckel), except that the two distal chambers are somewhat smaller than the proximal pair. Pores of the proximal chambers subcircular, 3-6 times as broad as the intervening bars, 13-15 on a half equator, 7-9 on the length of a chamber. Walls of the proximal chambers bearing large, obtuse protuberances, 1.5-2 times as broad as the pores and half as long, usually concentrated on the widest part of the chambers. Pores of the distal chambers similar to those of the proximal, except for a row of larger pores at the junction with the latter. Surface of the distal chambers usually covered with short, acute, conical spines, approximately as long as the diameter of the of the pores. External medullary shell compressed, its greatest diameter half the equatorial diameter of the cortical shell; the inner medullary shell not clearly visible.

Total length of the shell 162-180 Ám; of the apical spines 2-6 Ám. Maximum breadth of the proximal cortical chambers 80-85 Ám; of the distal cortical chambers 65-75 Ám; of the equatorial constriction 70-75 Ám; of the external medullary shell 32-35 Ám.

This species differs from all other of the genus in the heavy protuberances on the proximal chambers of the cortical shell. Apart from this character, it corresponds closely to the cosmopolitan Recent species Panartus tetrathalamus Haeckel and P. quadrijugus Haeckel. There is also considerable similarity to P. tetrameres Haeckel from the late Tertiary of Caltaisetta, Sicily.
Riedel 1953











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