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Diartus petterssoni (Riedel and Sanfilippo, 1970)

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Cortical shell rather thick-walled, approximately cylindrical (sometimes bulged at the equator), with pronounced protuberances surrounding each end of the cortical shell. Pores of the cortical shell circular or subcircular, smaller near the equator. Two medullary shells, of which the outer is commonly spherical, sometimes lenticular. Very broad spongy columns (in some specimens divided into naroow parallel zones) are separated from the cortical shell by a narrow clearer zone: the distal margin of this clearer zone is commonly at the end of the protuberances.
Length of spongy columns 25 to 100µ (commonly about 50µ); their median breadth 50 to 85µ. Length of cortical shell 80 to 100µ; its maximum breadth (including protuberances) 75-95µ. Breadth of outer medullary shell is 25 to 40µ. (Measurements based on specimens from PROA 96P, 227 to 230cm and SDSE 87, 799 to 800cm.)
Remarks: Although the spongy columns of some specimens shows parallel zones, these are not distinct caps as in Ommatartus hughesi.
(Riedel and Sanfilippo) 1970











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