Diagnosis: Calcitic shells. Small to fairly large sized, varying from fusiform to very widely ovate. Typically nonvaricate, but strong axial sculpture may be present. Sculpture absent, nodulose or spiny, never ramose. Siphonal canal short to absent, open. Central tooth of radula with 5 cusps (occasionlly 3). Operculum with lateral nucleus.

Remarks: This was a neglected group until fairly recent times and was known as the Thaidinae, or sometimes raised to full family rank, the Thaididae (as well as the Purpuridae). Kool (1993) demonstrated that the correct name for this group was Rapaninae or Rapanidae. The rapanines seem to be an intertidal or shallow water invasion of the Muricidae, often into boreal habitats. Like many intertidal species, their shell shape and physiology are often very different from their offshore relatives -- the product of pounding waves and possible desiccation. 

The generic and subgeneric status of many species remains unclear, at least to me. I agree with Keen (1971): "Subgeneric divisions are not easy to distinguish, and some assignments are rather arbitrary."

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