Crustacea glossary

CARAPACE COSTAE

Closely spaced radial ridges, grading from fine to coarse, that become obsolete near umbo and do not cross it (=radial lirae, radial riblets, accessory ribs) (e.g., Conchostraca, especially Estheriellidae, in which valves generally have more than 5 costae) [Moore and McCormick, 1969].
(Order Diplostraca):
Closely spaced radial ridges, grading from fine to coarse, not crossing to umbo. (Syn. radial lirae) [McLaughlin, 1980].

  1. carapace costae—ARTHROPODA Crustacea Fine to coarse closely spaced radial ridges that do not cross the umbo radial lirae....Dictionary of invertebrate zoology