A Grammatical Dictionary of Botanical Latin

Costula,-ae (s.f.I), abl. sg. costula, nom.pl. costulae, acc.pl. costulas, dat. & abl.pl. costulis: costule, a small rib or ridge, such as in the sculpturing of a mollusc shell; the midrib of fern-pinnae; secondary ribs [> L. dim. of costa,-ae (s.f.I), q.v.];

- sori indusiati; indusia hemiteliiformia, dorso costulam tangentia, sori indusiate; indusia like those of Hemitelia, at the back touching the costule.

- costulae inter se 3 mm. (steriles) vel 2 mm. (fertiles) distantes, the costules between themselves 3 mm. (sterile) or 2 mm. (fertile) apart.

- costulae infra paleis minutis vestitae, the costules below clothed with minute scales (paleae).

- petiolis in costulas internodii decurrentibus, with petioles decurrent into internodal costules.

- sori inframediani, secus costulam dispositi, the sori below the middle, arranged along the costule.

- sori uniseriati exacte inter marginem et costulam intermedii, sori in a single series exactly halfway between the margin and costula (Stearn).