No, this is not a Cytherella. It is a right lateral view of a carapace of a bairdioidean. Some would call it Bairdia but that has become rather a bucket genus. If you have  disarticulated valves you can look for the auxiliary dentition of Bairdoppilata. I can't see any terminal denticulation so it is unlikely to be Neonesidea or Paranesidea. Consult Maddocks (1969) Revision of Recent Bairdiidae for further information. I don't have my copy to hand, but it may help you. You don't say how many microns the scale bar is. guess 100?

Thank you so much  Dr. Ian J slipper  for your informative input. Image scale bar = 200μm. Ya I am very much convince with your answer  yes, it is Bairdia .

Please keep in mind that, like Dr. Slipper already said, Bairdia is a bucket genus. However, previous reviews of this genus suggest it was restricted to the Paleozoic Era. Considering your material is Paleocene, it would be safer for you to call it Bairdiidae sp.

Lucas Antonietto thank you for your input. I will keep it mind... I am still consulting more litreature and  trying for correct taxonomic identification.

Dear Lucas Antonietto and Ian Dr. J Slipper what about Bairdia ilaroensis Reyment and Reyment, 1959 which external morphological feature is much more similar to attached specimen and it's geographic and stratigraphic distribution are as  -  in Senegal, Mauritanian basin( off west Africa): Paleo-cene to middle Eocene - Côte d’Ivoire: Paleocene - Togo andBenin: upper Paleocene to lower Eocene - Nigeria and Niger:Paleocene - Mali: Maastrichtian to Paleocene - Tunisia, Libyaand Egypt: upper Paleocene to lower Eocene.  See here I am attaching both valve lateral view image.  Kindly provide your observation.

Dear Sanjay,

I agree with all, your specimen might be a Bairdia ilaroensis.

Best regards,

Hakima

 Thank you so much   Dr.  Hakima Belkhattab  for your  input.

 Regards

 Sanjay

You are welcome dear!

Cordially,

Hakima

I am much inclined to the genus Bairdia, particularly if your specimen from Paleocene. here the attached is Bairdia ilaroensis Reyment and Reyment from my Samples