Crematogaster (Crematogaster) impressa Emery

Type location Cameroun (Emery, 1899e: 486, worker & queen; Forel, 1916: 408, male) collector Conradt - see below
junior synonyms (here)
brazzai (Crematogaster impressa Em. stirps Brazzai, n. st., Santschi, 1910c: 373, worker & queen) from Congo, Brazzaville by A. Weiss - see http://www.antweb.org/specimenImages.do?code=casent0912683 - an exact match
andrei (Cremastogaster excisa Mayr subsp. Andrei n. subsp., Forel, 1911f: 277, worker & queen; note confused status, Wheeler, 1922: 836; synonymy by Santschi, 1937b: 99) from Zaïre at Congo da Lemba, by R. Mayné - see https://www.antweb.org/specimenImages.do?code=casent0908522
aglaea (Crematogaster excisa subspecies impressa (Emery) variety aglaea Santschi, new variety, in Wheeler, 1922: 153, worker) from Ivory Coast, at Dimbroko, by Le Moult - see http://www.antweb.org/specimenImages.do?code=casent0912681
euphrosyne (Crematogaster excisa subspecies impressa (Emery) variety euphrosyne Santschi, new variety, in Wheeler, 1922: 153, worker) from Faradje, Zaïre, Lang & Chapin - see  http://www.antweb.org/specimenImages.do?code=casent0912658
pensitata (Cremastogaster excisa Mayr r. Andrei For. v. pensitata n. var., Forel, 1915c: 341, worker) from South Africa - no images on Antweb (August 2016) - the location suggests the synonymy may be incorrect
See Bolton, 1995); all forms described .

Distinctly different being smaller and yellow-brown is Crematogaster (Cr.) maynei and its junior synonym sapora; both are light brown and with dense fine spiculation on head and alitrunk

Emery's (1899e) description is at . Santschi's (1910c) description of brazzai is at . Forel's (1911f) description of andrei is at . Forel's (1913h) description of maynei is at . Forel (1915c) has pensitata as smaller, TL 2.6-3.0 mm, than andrei and wholly black. Forel's (1916) description of the male and of sapora is at .

Emery's description was as a perhaps extreme subspecies of Crematogaster tricolor. C. impressa however had shorter scapes and much shorter propodeal spines. The sculpturation overall was much finer. Last but not least it was wholly black apart from reddish trochanters and tarsi.

Wheeler's (1922) description is -
Crematogaster excisa subspecies impressa (Emery) variety aglaea Santschi, new variety, the longitudinal rugae being feebly or not at all indicated. Head and thorax narrower. Promesonotal impression feebler as in euphrosyne, with a small carina on the front of the mesonotum, which is sharply marginate, less concave than in andrei (Forel) and more so than in impressa (Emery). Basal surface of the propodeum scarcely broader than the petiole. Spines almost as long as the interval between their bases. Anterior angles of petiole truncated as in andrei. Otherwise like impressa (Emery). "Dimbroko, Ivory Coast (Le Moult)." In impressa the funiculi are brownish black and in andrei the mesonotal carina is lacking." (Santschi).
Also
Crematogaster excisa subspecies impressa variety euphrosyne Santschi, new variety.
"WORKER.Length 3.5 mm. More or less pale chestnut brown. Thorax narrow. Pronotum reticulate-punctate in the spaces between the fine longitudinal rugae. Mesonotum feebly carinate in front. Resembles the variety brazzai Santschi, but the latter has a broader thorax, without carina and the sculpture of the thorax is merely reticulate." (Santschi).

Forel (1911f) described andrei (as a subspecies of excisa) - TL 3-3.88; colour black with slightly brownish hint, antennal club and tarsi reddish. Propodeal spines (almost twice as long as the type) as long as the space betwen the bases. Thorax entirely matt, more densely reticulo-punctate, with several fine longitudinal rugae. Apical two segments of antennal club relatively slender; remainder similar to excisa. Specimens from Zaïre, Congo da Lemba, by Mayné; plus females from "Congo" by M. André. He noted the type (excisa) is ferruginous red, and andrei is separable by its colour and long propodeal spines; M. André had sent him the specimens as an unknown form, but being unwell had asked him to describe and name the specimens. The type specimens show andrei to be almost identical in colour, dark brown, and form, just a little smaller.

The photomontage of the type worker collated from http://www.antweb.org/specimen.do?name=casent0904517

Wheeler (1922, as an ssp of excisa) also listed Ivory Coast (Bassam by Bonhouse) and Congo areas. The workers were found in hollow twigs; apparently a characteristic of the species is a very densely punctate pronotal dorsum, with feeble longitudinal rugae, TL 3.5 mm. Bequaert (1922, p 492) listed it, as Crematogaster excisa ssp andrei (Forel), from a Cuviera. Forel (1909b) noted E. André had asked him to identify Crematogaster from Congo collected by Father Hermann Kohl and Professor Laurent, botanist, from in the stems of plants. These included this species, samples No. 111 & 116, from Kisangani [Stanleyville] in the twigs of Bucherodendron speciosum and Barteria fistulosum..

Santschi (1935) also saw workers from Lundu, Lukula, Kidada-Kitobola and Bakusu, Zaïre; with the specimens from the last nesting in Trema guineense. He recorded andrei from Haut Uele, Moto, noting that this form is distinguished by the head being more strongly and completely striated. Under excisa, he noted the pronotum has raised lateral borders.

Bernard (1952) noted this small brown species was common in western Africa and Monod had found it nesting in hollow stems in Niger. From Guinea, in the Mt. Nimba surveys it was one of the most abundant genus members in lower areas, up to 700 m, but entered the primary forest with difficulty, e.g. at Ravine I of Mount Tô.

Oxford University Museum specimens

Crematogaster (Crematogaster) impressa B Taylor det.	Liberia E Poirier Yekepa Camp 4 PF 2	6.iv.2013 Nimba County 07°33’04" N 08°33’17" E	Pitfall trap Floodplain & marsh 501 m asl	4
Crematogaster (Crematogaster) impressa B Taylor det.	Liberia E Poirier Yekepa Camp 4 PF 14	6.iv.2013 Nimba County 07°33’04" N 08°33’17" E	Pitfall trap Floodplain & marsh 501 m asl	1
Crematogaster (Crematogaster) impressa B Taylor det.	Liberia E Poirier Yekepa Camp 4 PF 16	6.iv.2013 Nimba County 07°33’04" N 08°33’17" E	Pitfall trap Floodplain & marsh 501 m asl	1

The photomontage is of a worker collected in Liberia, Yekepa Camp 4;  collector E Poirier (Yekepa Camp 4 PF XIV).