dorsal sepal 5-nerved, not 8-nerved, 4) lip with four 
lamellate calli instead of two, 5) petals 38-nerved not 1- 
nerved. 
Pleurothallis involuta L. O. Williams sp. nov. 
Herbae perparvae, repentes vel caespitosae, epiphyti- 
cae. Folia elliptico-ovalia vel ovalia, obtusa vel plusmin- 
usve acuta, marginata. Inflorescentia uni- vel pauciflora, 
quam folia longior. Sepalum dorsale naviculare, oblongo- 
lanceolatum, acutum, uninervium. Sepala lateralia basi 
plusminusve libera, obliqua, oblongo-lanceolata, uni- 
nervia. Petala anguste rhombica, acuta, leviter obliqua. 
Labellum lanceolatum, obtusum, leviter naviculare, cil- 
iatum, basi biauriculatum, bicallosum. Columna generis. 
Very small, repent or apparently caespitose, epiphytic 
herbs. Secondary stems very short, about 1 mm. long. 
Leaves elliptic-oval to oval, obtuse or somewhat acute, 
marginate, 4-6 mm. long, 2.5-4 mm. broad. Peduncle 
up to about 15 mm. long, much exceeding the subtend- 
ing leaf. Inflorescence a one- to few-flowered raceme. 
Dorsal sepal about 2—2.5 mm. long and 1 mm. broad, 
navicular, oblong-lanceolate, acute, 1-nerved. Lateral 
sepals about 2—2.5 mm. long and 0.75-1 mm. broad, 
free nearly to their base, obliquely oblong-lanceolate, 1- 
nerved. Petals narrowly rhombic, acute, slightly oblique, 
obscurely 1-nerved, about 2 mm. long and 0.75 mm. 
broad. Lip lanceolate, obtuse, somewhat navicular, cili- 
ate, biauriculate at the base, the auricles membranaceous, 
with a callus-thickening on either side of the middle 
which extends from the base to the apex and is involute 
toward the apex, about 1.5—-2 mm. long and 0.5-0.75 
mm. broad. Column about 1.5 mm. long, shorter than 
the petals. 
Mexico: on tree trunks and branches, malpais near Urupdan, State 
of Michoacan, at 1700 meters altitude, petals and lip brown, sepals 
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