Calosoma (Callistenia) luxatum Say, 1823

Length 13-23 mm. The pronotum of C. luxatum is a little narrowed behind, slightly heart-shaped and with acute hind angles, a little protruding from the base line. The elytron has 15 intervals (triploid type). The intervals are distinct, have the same width and are conformed in the same way, usually consisting of a series of subquadrate or rounded small elevations, separated by transverse wrinkles. The striae are not always visibly punctate..
C. luxatum is a very variable species and this variability, as in the case of C. discors, gave rise to the description of many forms, variously interpreted by the authors.
Of these forms, Gidaspow (1959) had reassessed as good species, within her genus Callisthenes, subgenus Microcallisthenes, the followings: zimmermanni, lariversi, monticola, subasperatus and pimelioides
Callisthenes (Microcallisthenes) zimmermanni should essentially differ from C. luxatum because of its pronotum that is much narrower behind. It was regarded by Breuning (1927) as subspecies but was placed in synonymy by Jeannel (1940:173), whose opinion was shared by the subsequent authors (Lindroth, 1961: 55; Erwin, 2007: 78). The same happens with Callisthenes (Microcallisthenes) pimelioides that Gidaspow emphasized as a distinct species because of some minor differences in the chaetotaxy of the head and of the pronotum. However these differences do not seem to be costant (Lindroth, 1961: 55) and now almost the totality of authors consider pimelioides a synonym of luxatum.
With regard to other forms, Callisthenes (Microcallisthenes) monticola, and Callisthenes (Microcallisthenes) subasperatus can be differentiated between them and from the typical form, only for the chaetotaxy (mostly in terms of frequency statistics) and in particular presence and number or absence of the pronotal setae and of the supraorbital ones. In this case too we are dealing with incostant characters that can vary from individual to individual and consequently both taxa were considered by Breuning (1927) as individual aberrations and as synonyms of luxatum by Jeannel (1940: 173).
Callisthenes (Microcallisthenes) lariversi, described by Van Dike (1943), is characterized by the pronotum almost smooth and by the sculpture of elytra very flat, almost obliterated, where only the striae are indicated by series of small dots. The elithral sculpture within the luxatum populations, as indeed happens in other species of Calosoma, is not in itself a decisive character. In fact, it is individually very variable and only rarely it represents an identifier of entire populations. More in-depth analyzes would therefore be needed to assess its isignificance
Finally, Gidaspow (1959) also described a further species: Callisthenes (Microcallisthenes) oregonus, which which should be distinguished because of a slender body shape and minor differences in the shape of the apex of the penis and of the ligule, which also in this case we do not consider sufficiently defined to characterize a distinct taxon.
All these forms come together in the same distribution area of the typical one along the ridge of the Rocky Mountains and, in order to take into account the sympatry, the current opinion is that at least some of them are distinct species.
However, the overlap of habitats, does not rule out the possibility of simple isolated populations, including the transitional forms in the areas of contact.
Alternatively, if we take into account the small differences between the various described forms, especially when confronted with the great differences that we find between individuals inside of each populations, we might consider most of these forms, as simple expressions of individual variability within a single species.
Because of all these considerations, we think that it is preferable, at least for the moment, to do not use further distinctions within the specific complex of luxatum, according to the opinion already expressed by the ancient authors about most of the described forms.
The only possible exception is the case of lariversi, which seems only being found in the Great Basin desert, and that undoubtedly belongs to the luxatum group, as already noted by Gidaspow (1959: 314), but which could well constitute a separate subspecies, geographically isolated.
All the populations that, basing on these criteria, can be attributed, for whatever reason, to luxatum, are found along the chain of the Rocky Mountains and the Sierra Nevada, from southwestern Canada to all the western United States.

Examined specimens and literature’s data
Canada. Alberta: Medicine Hat (sub zimmermanni, SB), Stanley (EM), Calgary, Tilley, Jenner, Hilda (Gidaspow 1959: 311), 20.9 km north Hanna (UASM), Crowfoot, Manyberries, Ralston, Oldman River (UASM), 4.2 km W Empress (UASM), Jenner, Brooks (Lindroth, 1961: 56); British Columbia: Osoyoos (Haynes Point) (UASM), Vancouver island (sub zimmermanni, Breuning 1928b: 85), Okanagan-Similkameen (www.inaturalist.org/); Saskatchewan: Pike Lake (SB), Saskatoon, Forget (Gidaspow 1959: 310), Beaver Creek, Radisson (Lindroth, 1961: 56).
United States. Arizona: Grand Canyon (Gidaspow 1959: 311); California: Nevada County (EM), Eldorado Co. (Gidaspow 1959: 311), Antelope Valley (www.inaturalist.org/), Alpine Co., Inyo Co., Sonoma Co., Tuolumne Co., (sub zimmermanni, Gidaspow 1959: 318), Placer Co., Lassen County, Ventura Co. (Point Mugu N.P.), San Diego County, Modoc County (www.inaturalist.org/), Plumas Co., Mono Co. (Sonora Pass), Shasta Co. (UASM), Humboldt Co. (sub zimmermanni, Gidaspow 1959: 318); Colorado: Arkansas river, Denver, Fort Collins (Breuning 1928b: 85), Glenwood (Gidaspow 1959: 311), Moffat County, Pawnee National Grassland (www.inaturalist.org); Idaho: Ada County (www.inaturalist.org/); Elmore Co. (Atlanta) (sub zimmermanni, Breuning 1928b: 86), Gooding Co. (sub zimmermanni, Gidaspow 1959: 318), Bannock Co. (Gidaspow 1959: 311), Owyhee county, Cassia county, Lincoln Co. (8 km N Dietrich Butte), Bingham Co (Blackfoot)(UASM), Bruneau Dunes State Park, Boise (www.inaturalist.org/); Montana: Lewis and Clark Co. (Augusta) (Jeannel, 1940:176), Gallatin Co, Three Forks, Milk river (Gidaspow 1959: 311) Silver Bow Co, (26.7 km S Butte) (UASM); Nebraska: Brown Co., Kashopa, Sioux Co., Hat Creek Valley (Gidaspow 1959: 311), Dawes County (www.inaturalist.org); Nevada: Humboldt co., Washoe co. (sub zimmermanni monticola), Lander co. (sub zimmermanni nevadense), Elko co. (sub lariversi) (La Rivers, 1946: 136-137), Elko County, White Pine County, Mineral County, Washoe County, Lyon County (www.inaturalist.org/); New Mexico: Cibola county (www.inaturalist.org); Oregon: (holoype of Carabus opacus) (MNHN), Harney Co., Jackson Co., Malheur Co., Gillam Co., Deschutes Co. (www.inaturalist.org/), Benton Co., Grant Co., Klamath Co., Lake Co., Polk Co., Umatilla Co., Wallowa Co., (Gidaspow 1959: 311) Baker Co. (Wallowa-Whitman National Forest) (UASM), Dalles/Deshutes River (http://bugguide.net/); South Dakota: Fall River County (www.inaturalist.org/); Utah: Daggett County, Fairfield, Utah Co. (Lehi), Davis County (www.inaturalist.org/), Tooele Co., Wasatch Co., (Gidaspow 1959: 311) Cache Co. (6.4 km W Mendon) (UASM); Summit Co. (Park City), Grand Co. (Cisco) (sub zimmermanni, Breuning 1928b: 85); Washington: Whitman Co. (Pullman) (SB), Adams Co., Franklyn Co., Yakima Co., (Gidaspow 1959: 311), Benton Co (24.0 km W Paterson) (UASM), Kittitas Co., Rattlesnake mountain, Oak Spring, Lyle (Klickitat Co.), Kennewick (Walla Walla Co.), Douglas Co., Othello (Grant Co.) (www.inaturalist.org/); Wyoming: Carbon Co. (Como) (Breuning 1928b: 85), Yellowstone National Park (Jeannel, 1940:176), Laramie Co. (Gidaspow 1959: 311), Albany County, Natrona County (www.inaturalist.org/).

Notes: Brachypterous. It is found from midlands to alpine zones, from 800 to 4000m altitude, on praries and on open ground in dry forests. It is mainly nocturnal and is rarely seen during the day when it preferably takes refuge under stones or is found in shallow depressions or cavities that it has dug itself. According to the material examined, the adults are active from February to July with a maximum in April-May, but, depending on the characteristics of the different habitats, they can remain active up to September (Erwin, 2007: 76 - 82).

Calosoma (Callistenia) luxatum ♂ Say, 1823 Canada: Alberta, Medicine Hat, V. 18

Calosoma (Callistenia) luxatum ♀ Say, 1823 United States: Washington, Pullman, March 27 1899

Callisthenes (Microcallisthenes) zimmermanni ♀ (LeConte, 1848) Oregon, Washington (Typus) (coll. and photo: Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA) a synonym of Calosoma (Callistenia) luxatum Say, 1823

Callisthenes (Microcallisthenes) zimmermanni ♀ (LeConte, 1848) Etats Unis, Oregon, (holoype of Carabus opacus Géhin, 1885) (coll. Muséum National d'Histoire Naturelle, Paris) a synonym of Calosoma (Callistenia) luxatum Say, 1823

Callisthenes (Microcallisthenes) oregonum ♀ Gidaspow, 1959 (photo: Mackenzie Flight) most probably a form related to Calosoma (Callistenia) luxatum Say, 1823

Callisthenes (Microcallisthenes) monticola ♀ Casey, 1913 (photo: Mackenzie Flight) most probably a form related to Calosoma (Callistenia) luxatum Say, 1823

Callisthenes (Microcallisthenes) subasperatus ♀ Schaeffer, 1915 (photo: Mackenzie Flight) most probably a form related to Calosoma (Callistenia) luxatum Say, 1823

Callisthenes (Microcallisthenes) lariversi ♂ Van Dike, 1943 Nevada, Lamaille, 25.VI.41, La R., coll. Van Dike (Typus) (coll. and photo: California Academy of Sciences, San Francisco) most probably a form related to Calosoma (Callistenia) luxatum Say, 1823