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Hyolithida - Similothecidae
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.
|J. M. Malinky and C.B. Skovsted 2004||Similotheca with dorsum having one narrow, keel−like ridge on each flank and coarse,widely spaced rugae.
Description.—Conch seemingly orthoconic with large apical angle such that conch expands rapidly; venter inflated into broad, rounded surface; lateral edges sharp and keel−like; dorsum high and inflated with median ridge marked by central longitudinal keel−like rib and one similar keel in the middle of each flank; surface of flank is concave next to both the central rib and the rib in the middle of each flank, whereas elsewhere the flank is convex. Dorsal apertural rim orthogonal but with very shallow median indentation, and lateral sinuses broad though shallow; ligula long and curved atanterior edge with steeply dipping sides. Cross−section has
rounded triangular shape.
Dorsum covered with transverse rugae that are widely separated and irregularly spaced; each is rounded on top with gently dipping sides such that interspaces are curved on both sides; combination of rugae and keels defines cancellate pattern on dorsum. Venter with faint growth lines only.