Definition: A taxon is Extinct when there is no reasonable doubt that the last individual has died. A \r\ntaxon is presumed Extinct when exhaustive surveys in known and/or expected habitat, \r\nat appropriate times (diurnal, seasonal, annual), throughout its historic range have failed \r\nto record an individual. Surveys should be over a time frame appropriate to the taxon’s \r\nlife cycle and life form.
Definition: Repeated, thickened, raised structures on the shell or carapace surface, comparable to or greater than the thickness of the shell/carapace and covering a notable portion of it. Thickenings can be either radial, comarginal, axial or spiral.