| 21. | The siphuncle is displaced from the center slightly toward the venter.
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| 22. | Septa are close spaced, the siphuncle is small and ventrally located.
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| 23. | The siphuncle is prochoanitic, with septal necks projecting forward.
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| 24. | The siphuncle is broadly expanded, and in some actinosiphonate.
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| 25. | The siphuncle is small, tubular, and subcentral . ( 1964)
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| 26. | The siphuncle of " Oonoceras " is cyrtochoanitic.
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| 27. | The subcentral siphuncle contains vesicular deposits and a central tube.
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| 28. | The siphuncle is located midway between the center and venter.
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| 29. | Siphuncle segments are short and well expanded into the chambers.
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| 30. | Some poterioceratid genera have actinosiphonate structures or annular deposits within the siphuncle.
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