|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||Age range and collections|
Hyolithida - Hyolithidae
If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
|L. R. Babcock and R. A. Robison 1988||Hyolithid with weak, longitudinal, dorsornedial septum in conch. Lateral longitudinal sulci singly paired on dorsum and venter.
Conch with single septum along inner dorsomedial surface, formed by thickening where slopes meet. Dorsum subangular, slopes subtly convex. Apical end slightly turned dorsally and laterally, usually to right. Lateral margins angular. Lateral longitudinal sulci singly paired on dorsum and venter, extending along entire length of shell. Venter slightly inflated. Ligula short, narrowly rounded. Apertural rim not flared. Aperture probably orthogonal. Growth lines fine, better developed on venter than dorsum.
Operculum questionably platyclaviculate; outline ovate, broad; apex bluntly pointed. Conical shield large, subtriangular; lateral sides nearly straight; ventral side broadly rounded. Cardinal shield broad, cardinal processes large. Growth lines and rugae present on shields, absent on rooflets.
Helens very thin, arcuate with slight vertical twist, tapering proximally and distally. Length along curve about 0.45 times maximum conch length, width about 0.06 times length. Growth lines fine, equally developed on both sides.