Bembidion laxatum, CASEY, 1918

Sproul, John S. & Maddison, David R., 2018, Cryptic species in the mountaintops: species delimitation and taxonomy of the Bembidion breve species group (Coleoptera: Carabidae) aided by genomic architecture of a century-old type specimen, Zoological Journal of the Linnean Society 183, pp. 556-583 : 576-577

BEMBIDION LAXATUM CASEY

( FIGS 1D, 8G, H, 10H, 11H, 12B, 13E, F, 15B)

Bembidion laxatum Casey, 1918: 24 . Lectotype male, designated by Lindroth (1975: 117), in USNM, labelled ‘Placer Co. CAL.’ [white paper], ‘CASEY bequest 1925’, ‘TYPE USNM 36833’ [red paper], ‘laxata Csy.’ [white paper, handwritten], ‘ LECTOTYPE laxatum Csy. By C.H. Lindroth’ [white paper, partly handwritten]. Type locality: Placer Co., California. Examined, including genitalia.

Bembidion adumbratum Casey, 1918: 26 . Lectotype male, designated by Lindroth (1975: 117), in USNM, labelled ‘Placer Co. CAL.’ [white paper], ‘Oct.’ [white paper], ‘CASEY bequest 1925’ [white paper], ‘TYPE USNM 36827’ [red paper], ‘adumbrata Csy.’ [white paper, handwritten], ‘ LECTOTYPE adumbratum Csy. By C.H. Lindroth’ [white paper, partly handwritten]. Type locality: Placer Co., California. Examined, including genitalia.

Bembidion rainieri Hatch, 1950: 97 . Holotype female in USNM, labelled ‘Mt. Rainier, WASH. Sunrise Park Sept. 6, 1934 M. H. Hatch’ [white paper], ‘ADP 115747’ [white paper], ‘ Bembidion (Plataphodes) laxatum Csy. M. Hatch-1969’ [white paper, handwritten], ‘TYPE Bembidion (Trechonepha) rainieri 1948.- M. H. Hatch’ [red paper, hand written]. Examined. Type locality: Sunrise Park, Mount Rainier Pierce Co., Washington.

Diagnosis: Large and heavy-bodied, this parallel-sided species is distinct in its dull appearance, particularly females. Forebody and hindbody dark brown, rarely black, typically with aeneous, or bluish, metallic hue. Pronotum broad and somewhat convex; widest near middle with hind angles near 90° or slightly obtuse ( Fig. 11H); laterobasal carina strong ( Fig. 12B). Elytra widest near middle, often narrowing towards apex; elytral striae somewhat pronounced, and dorsal punctures moderately foveate ( Fig. 1D). Microsculpture strongly etched in males; very strongly etched, often granulate, in females ( Fig. 13E, F). Male genitalia with short, weakly sinuate flagellum; sclerite ‘St’ with U-shaped recurvature ventrally ( Figs 8G, H, 10H).

Comparison with similar species: Most easily confused with B. oromaia from which it is distinguished by having a wider pronotum relative to width of the elytra, the elytra being widest near middle, having larger protarsomeres in males, less slender, elongate legs and antennae, and by various characters in the male genitalia. May also be confused with B. lividulum and B. ampliatum . It can be distinguished from both by its larger, more convex body, duller appearance due to strong microsculpture in both sexes, broadened pronotum relative to the elytra with hind angles near 90°, and the U-shaped recurvature of sclerite ‘St’ in the male genitalia.

Geographic distribution: Throughout the Sierra Nevada in California, north along the Cascade Range to Washington and southern British Columbia ( Fig. 15B).

Habitat: Open alpine slopes commonly below patches of melting snow or along small alpine creeks.

Geographic variation: Sclerite ‘St’ in males from California localities is fairly elongate ( Fig. 9G, H). Sclerite ‘St’ in the few Washington and British Columbia specimens available for examination appears slightly less elongate and more broadened than in California specimens.