Dicaelus (Paradicaelus) ambiguus La Ferté-Sénectère 1841

Dicaelus (Paradicaelus) ambiguus Laferte
Dicaelus ambiguus Dejean, 1837:31; [nomen nudum].
Dicaelus ambiguus Laferte, 1841 : 44.— Ibid., 1851 : 277.— Le Conte, 1873:324.
Dicaelus opacus Laferte, 1841:43; Type locality: "Texas"; (determined from original description). — Le Conte, 1873:324. — Loding, 1945:18.
Dicaelus reflexus Le Conte, 1848:330; [type specimen a male, in Le Conte Coll., MCZ no. 5717]. Type locality: Columbia, Pennsylvania; (determined from original description). — Ibid., 1873:324.
Dicaelus turbulentus Le Conte, 1863: 12; [type specimen a female, in Le Conte Coll., MCZ no. 5718]. Type locality: Missouri; (collected by Prof. Agassiz; determined from original description). — Horn, 1880: 52.
This species most closely resembles D. teter but may be distinguished from it by the following characters as well as by those which are presented in the key : lateral margins of pronotum more strongly reflexed, not strongly sinuate posteriorly and surface of head and pronotum rugulose to moderately rugose.
Variation. — Size variation was not studied in detail because of the paucity of available material. Data on variation in width and in the ratios PN : W/L, and W base/W apex of a series of twenty males and twenty females, chosen from localities scattered throughout the range of this species, are presented in tables 21, 22, and 23. The latter ratio is useful in separating this species from D. teter.
Lustre of the integument varies from opaque to somewhat shining, but never as shining as is average for D. teter, and the variation seems to be of an individual, rather than of a population, nature. Shape of the pronotum and degree of upturning of the sides varies slightly. Smaller specimens tend to have the pronotum more strongly flanged than larger specimens. Of forty specimens examined, thirty completely lack the lateral beading on the pronotum ; in five specimens the bead is about 1/4 of the total length of the pronotum, and in the five the beading extends for about 1/2 the length of the pronotum. The length of the carinate portion of interval 7 varies from an average of about 1/3 of the total length of the elytra, to about 1/2 in a specimen collected at South West, Arkansas (Amer. Mus. Nat. Hist. Coll.). The median lobe (fig. 109) exhibits slight variation in shape of the apical portion.
One specimen, a male collected at Bard Springs Camp, Ouachita Mountains, Polk County, Arkansas, August 15, 1951, by T. J. Cohn, is quite different from all of the other specimens which I have referred to this species. The pronotum is cordate in shape, resembling, to some extent, D. teter. The carina of the 7th interval extends for 2/3 of the total length of the elytra and the elytra are flatter than usual. It is thus quite different in appearance from the average run of this species. However, the dorsal surface of the left mandible bears the usual tubercle and the genitalia are typical for D. ambiguus. The following irregularities of the pronotum suggest that this specimen may have had an abnormal development : right anterior margin with a noticeable undulation, median longitudinal impression bent slightly to left before midline.
Synonymical Notes.— Le Conte (1873) established the synonymy presented above and used ambiguus as the name for this species, even though opacus Laferte was the senior synonym. Since his study was, in essence, a revision of the species, Le Conte may be regarded as first reviser and as such had the privilege of choosing which name he pleased (see Article 28, Rules of Zoological Nomenclature, 1905). Therefore, the name ambiguus stands as the correct trivial name for this species.
The type specimen of turbulentus is a normal representative of ambiguus as Horn (1880) indicated.
Distribution. — This species ranges on the piedmont and coastal plain of eastern United States from northern Florida possibly to central New York, extending westward of the Appalachians across Pennsylvania to southeastern Iowa ; eastward along the coastal plain and piedmont to southeastern Texas, and in the eastern states of the Great Plains. Presumably it will be found southward in the temperate por
tion of northern Mexico, westward probably to the 100th Meridian, and northward to, but probably not much beyond, the southern limits of the Transition Zone forest.
I have collected this species in a beech-hemlock forest in Lawrence County, Alabama, in a mixed mesophytic forest in Tuscaloosa County, Alabama, in a moist situation.
I have examined sixty-two males and fifty-five females collected in the following states.
Peripheral localities — Pennsylvania : Monroe County, Water Gap. District of Columbia. Florida : Liberty County, Camp Torreya. Texas : Cameron County, Brownsville. Iowa : Lee County. Indiana : Tippecanoe County, Lafayette. Additional states — Alabama. Arkansas. Georgia. Illinois. Kentucky. Missouri. North Carolina. Ohio. Tennessee.

Dicaelus ambiguus is a species of ground beetle in the family Carabidae. It is found in North America.