It does not look like it... D. penultima has spongy columns after the first polar cap (not another series of polar caps). So this might be either D. tetrathalamus (the extant species of this genus), or some "odd" Miocene/Pliocene variety.
Sir,
Thank you for your comments . I think its not D. tetrathalamus as in tetrathalamus there are two medullary shells, but in my observed species there are three medullary shells. Did you came across this species before.
Agree to Cortese... It is more towards D. tetrathalmus as it does not have spongy columns at the polar caps. Specimen has 2 polar caps which is may be found in well preseved D. tetrathamus belonging to plio-pliestocene, or very oten pristine sediment trap material.
For example, specimens of Didymocyrtis penultima, D. antepenultima and Diartus hughesi, and other variants in their evolutionary linage may seen in plates of Gupta and Srinivasan, micropal. 38, 209, 1992, pdf attached
I agree with Giuseppe. If you think that your specimen has 3 medullary shells you are wrong. All species of this family group of radiolarians to which Didimocyrtis belongs have two medullary shells. Sometimes one can see only one or none when they are dissolved. But there are never three.
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