Species of Triquetrorhabdulus with c-axis perpendicular to length of nannolith. Typically these species are dark in cross-polarised light but they sometimes rest at angle where they show moderate birefringence they then show length-slow orientatons opposed to the lntgh-slow orientation of the T. carinatus group.

Typical specimens	Morphology	Range
	T. rugosus - the typical form	NN6-12
	T. rioi - parallel sided	NN6-7
	T. striatus - with subsidiary ridges parallel to long axis	NN10-12
	T. extensus - one blade extended into wing	NN11B-12
	T. finifer - arcuate shape	NN11B to 12