Xystosomus microtretus, Erwin, 1973

Erwin, Terry L., 1973, Studies of the subtribe Tachyina (Coleoptera: Carabidae: Bembidiini), Part I: A revision of the Neotropical genus Xystosomus Schaum, Smithsonian Contributions to Zoology 140, pp. 1-39 : 24

20. Xystosomus microtretus , new species

FIGURES 43 , 45 , 46 , 70

TYPE LOCALITY.— Hamburg Farm, Reventazón , Costa Rica.

TYPE-SPECIMENS.— The holotype male, allotype, and one paratype male are in USNM. They were collected by Nevermann in 1925, 1934, and 1932, respectively.

DESCRIPTION.—Form ( Figure 43 ): Medium-sized, broad, moderately convex (more so than X. gruti ), with small flat eyes, narrow head, broad pronotum, and square humeri. Easily distinguished from the other species of the group (see below) by the form of the pronotum.

Color: Head and body rufopiceous; pronotum and elytra moderately iridescent; appendages testaceous.

Head: Very broad between eyes; frontal furrows shallowly impressed posterior to clypeus, not prolonged onto frons beyond anterior margin of eye; eyes small, slightly prominent.

Pronotum ( Figure 43 ): Transverse (W/ L, x 1.58; range, 1.53-1.68; 3 specimens); lateral setigerous pores present only at hind angles; laterobasal carinae rudimentary; hind angles about 90°, sides anterior to angles more or less straight; side margins beaded, not reflexed.

Elytra: Each elytron with six rows of partially striate serial punctures and punctulae, rows 2-6 effaced before apex; side margins narrowly explanate; humeral projection absent, humerus evenly rounded; chaetotaxy as in X. gruti ; plica short, evident externally.

Microsculpture: As in X. gruti .

Secondary sexual characters: Male genitalia ( Figure 45 ) with internal sac quite different than in members of other species groups. Female genitalia ( Figure 46 ) characteristic of the species group.

Size: Three specimens: length, 3.3-3.6 mm; width, 1.6-1.7 mm.

NATURAL HISTORY.— Adults were collected in January and February. No teneral specimens were seen. Nevermann recorded the finding of these beetles from "under loose bark," "on forest soil," and "sifted from soil."

LOCALITY RECORDS ( Figure 70 ).—I have seen three specimens from the following locality: CENTRAL AMERICA: COSTA RICA: Hamburg Farm at Reventazon (USNM).

Figures

FIGURE 43.—Habitus of Xystosomus microtretus, male, Hamburg Farm, Costa Rica.

FIGURE 45.—Male genitalia, left lateral aspect, of Xystosomus microtretus, Hamburg Farm, Costa Rica.

FIGURE 46.—Female genitalia, ventral aspect, with spermathecal reservoir, of Xystosomus microtretus, Hamburg Farm, Costa Rica.

FIGURE 70 Approximate ranges of the elaphrinus group (crosshatched area) and the micro- tretus group (solid areas).