(Figs. 1, 2, 18)
Female. Body color: (Fig. 1) head black, occasionally with orange spots behind eyes, antenna dark brown to black, scape often orange at base; mesosoma black except pronotum dorsally, mesonotun and scutellum orange; metasoma black with apex of first tergum, second and third terga entirely, and fourth tergum at base frequently orange; legs orange, coxae sometimes dark brown; wings lightly dusky, veins including stigma brown. Body length: 7.5–8.0 mm; fore wing length, 6.0–7.0 mm. Head: eyes and ocelli small; 49–52 antennomeres, all flagellomeres slightly longer than wide; malar space longer than basal width of mandible and 2 / 3 eye height; temple equal to eye width; occipital carina complete, meeting hypostomal carina; oral space small and circular, width less than length of malar space and about 1 / 2 face height; clypeus swollen; ocelli small, ocellocular distance at least twice diameter of lateral ocellus; face rugose, short median ridge below antennae; frons and vertex rugose; temple coriaceous; maxillary palpus not swollen; mandible small, tips not crossing when closed. Mesosoma: pronotum rugose; mesonotum and scutellum coriaceous, notauli weakly scrobiculate, meeting before scutellum in wide rugose area; mesopleuron weakly rugulose, nearly smooth above episternal scrobe, subalar sulcus strongly rugose, sternaulus slightly impressed and strongly rugose; propodeum nearly horizontal, strongly rugose, apical corners protruding, median carina very strong and complete, almost like a lamellate ridge. Legs: tarsal claws long and slender, not pectinate but with long thin spines on basal 1 / 2; hind coxa coriaceous dorsally. Wings: slightly dusky; fore wing with vein r nearly 2 / 3 length of 3 RSa and nearly 3 / 4 length of mcu, second submarginal cell nearly square, vein 1 cua beyond 1 M by distance less than length of 1 cua (Fig. 18); vein 1 CUa 1.4 length of 1 CUb; hind wing with vein RS arcuate, marginal cell narrowest in middle, vein 1 rm shorter than 1 M, vein M+CU longer than 1 M, vein mcu indicated by short infuscated line. Metasoma: first tergum short and broad, distinctly shorter than apical width, rugose striate, median carina complete; second tergum rugose striate, median carina complete; third tergum rugose striate, median carina on basal 4 / 5; fourth tergum rugose striate on basal 1 / 2, coriaceous on apical 1 / 2; rest of terga coriaceous; ovipositor about 1 / 2 length of hind basitarsus.
Male. Essentially as in female; body usually entirely black, mesonotum often orange, coxae black.
Holotype. Female: NORTHWEST TERRITORIES, Hazen Camp, 81 ° 49 ’N, 71 ° 18 ’W, July 3, 1964, R. E. Leech. Deposited in CNC.
Paratypes. NORTHWEST TERRITORIES: 7 females, 7 males, same data as holotype with dates ranging from July 11, 1961 to July 2, 1964, collectors D. R. Olive, R. B. Madge and J. F. McAlpine; 1 female, 1, male, Eureka, Ellesmere Island, July 8–29, 1953, P. F. Bruggemann. YUKON TERRITORY: Tombstone C. G., July 10, 1977, Wharton coll. Deposited in CNC, USNM, RMSEL, TAMU.
Distribution. Known only from the northern Canada.
Biology. Pinned with the type series are caterpillar mummies (Fig. 2) that have subsequently been identified as the lymantriid Gynaephora rossii Curtis.
Comments. This species is similar in coloration to dichromatus but differs in the longer antennae, shorter first metasomal tergum and the position of vein 1 cua in the fore wing which is close to vein 1 M.
Etymology. The specific name is from the Latin aquilonius meaning northern or northerly in reference to the extreme northern locality of this species.