Octostruma limbifrons

The holotype was collected at a cloud forest site in western Panama, in a Berlese sample of forest floor leaf litter.

Identification
Antennal scrobe very shallow, not distinctly margined; face with arcuate carina; frontal carinae and facial arc separated, the termini of the facial arc extend laterally beyond the termini of the frontal carinae (termini of facial arc join frontal carinae in Octostruma ascrobis, Octostruma ascrobicula); facial arc strongly elevated and continuous to juncture with antennal socket, lateral portions of facial arc as strong as frontal carinae (facial arc weaker, lateral portions weaker than frontal carinae in Octostruma convallis, Octostruma convallisur); promesonotum with differentiated anterior and dorsal faces (evenly convex in O. convallis, O. convallisur). (Longino 2013)

Distribution based on Regional Taxon Lists
Neotropical Region: Panama.

Castes
Known only from the worker caste.

Nomenclature

 *  limbifrons. Octostruma limbifrons Longino, 2013: 39, figs. 6D, 29, 44 (w.) PANAMA.

Worker
HW 0.63, HL 0.59, WL 0.65, CI 106 (n=1). Labrum rectangular, formed of strap-like lateral portions joined by a thin translucent lamella; mandibles closed on available specimen, but appear generally similar to O. convallis; dorsal surface of mandible roughened, microfoveolate; scape flattened, with pronounced anterobasal lobe, dorsal surface smooth and shining; clypeus strongly emarginate anteriorly, smooth and shining; frontal carinae sharp, narrow, extending more or less straight back and ending before reaching transverse facial arc; facial arc strongly developed, forming continuous carina that curves forward to join posterior margin of antennal socket, with distinct trough between frontal carina and lateral facial arc; frontal carinae and facial arc delimit anterior face that is shiny, with distinct median longitudinal ruga and faint rugulae laterally, face immediately anterior to facial arc smooth, concave; compound eye small, circular, composed of 4–5 somewhat confluent ommatidia; side of head near compound eye and vertex posterior to facial arc smooth and shiny, with distinct, sparse, uniformly distributed puncta; antennal scrobe below eye, very shallow and not delimited with carina or flange; scrobe surface shiny, punctate; side of head posterior to scrobe completely smooth and shiny, with no puncta; undersurface of head rugose.

Promesonotum somewhat flat-topped, with distinct anterior face rounding into horizontal dorsal face; metanotal groove not impressed; propodeum with a single, concave, sloping surface, not differentiated into dorsal and posterior faces; propodeal spines acute, extending anteriorly as raised carinae that curve medially and join at the metanotal groove, extending ventrally as narrow lamellae, thus posterodorsal propodeum entirely delimited by raised carinae confluent with propodeal spines; a low carina extends transversely across posterodorsal surface, between bases of propodeal spines; propodeal spiracle large, located immediately below propodeal spine and abutting posterior margin; lateral, anterior, and dorsal pronotum smooth and shining with sparse puncta; mesonotum with denser puncta, sculpture differentiated from dorsal pronotum; posterodorsal face of propodeum shallowly foveolate; mesopleuron confluent with side of propodeum, shining, with smooth patches and feeble minute puncta and rugulae.

Petiole in profile with peduncle not differentiated from node, anterior surface sloping evenly from petiolar foramen to node, dorsal face of node sloping posteriorly to projecting transverse cuticular rim, short concave posterior face beneath rim; anteroventral margin with denticle; dorsal face of node faintly foveolate/punctate; postpetiole low, broad, crescent-shaped in dorsal view, dorsal face densely punctate, delimited anteriorly and posteriorly by thin transverse rim; first gastral tergite densely punctate, puncta becoming smaller posteriorly; first gastral sternite punctate with smooth and shining interspaces, puncta larger than on tergite.

Labrum fringed on sides and apex with soft translucent thick setae; each larger mandibular tooth with prominent fully appressed seta; anterior margin of scape with 7 stiff filiform (not clavate) setae, basalmost seta the longest, on apex of anterobasal lobe (lacking a shorter seta proximal to this one, on inner side of lobe); clypeus and face devoid of ground pilosity; face, dorsal mesosoma, petiole and postpetiole lacking erect setae; mesotibia with short, thin, sparse, decumbent ground pilosity, a single large filiform seta and several thin shorter erect setae at apex; mesobasitarsus with several pairs thin, erect setae, apical pair longest; first gastral tergite with 3 stiff filiform setae on posterior margin, following exposed tergites each with row of setae; ground pilosity of first gastral tergite sparse, fully appressed, length of setae subequal to distance between them; first gastral sternite with sparse, thin but stiff erect setae over much of surface except narrow area near postpetiolar insertion.

Color red brown.

Type Material
Holotype worker: Panama, Chiriquí: 24 km W El Hato del Volcan [8.833, -82.754, ±10 km], 1160 m, 26 Jun 1976, cloud forest, ex sifted leaf litter (A. F. Newton), unique specimen identifier MCZ-ENT00511414.

Etymology
The name refers to the strong facial arc. It is a noun in apposition and thus variant.