Stilpon mexicanus, Solórzano Kraemer & Sinclair & Cumming, 2005

Solórzano Kraemer, Mónica M., Sinclair, Bradley J. & Cumming, Jeffrey M., 2005, Five new species of Tachydromiinae (Diptera: Empididae s. l.) from New World Tertiary ambers, Zootaxa 1010, pp. 37-52 : 49-50

Stilpon mexicanus sp.n.

DIAGNOSIS. This species is readily distinguished from other Stilpon by the form of the antennae composed of an elongate pedicel bearing a pair of ventroapical bristles and a spatulate postpedicel. The row of posteroventral bristles and the preapical anterior bristle on the mid femur are also distinctive because of their length. In addition, S. mexicanus has A 1 slightly visible as a fold unlike all other known species of Stilpon , in which A 1 is absent ( Fig. 5).

DESCRIPTION. Female ( Fig. 5A). Length 1.6 mm. Head. Ground colour brown. Eyes with ommatrichia (pubescence); contiguous below antennae; facets slightly enlarged below antennae. Frons mostly parallel­sided; nearly parallel to slightly divergent above, narrow to wider than width of ocellar triangle. Two pairs of ocellar bristles; anterior pair convergent, inserted lateral to median ocellus and broadly separated; posterior pair inserted posterior to median ocellus and interval at base subequal to diameter of median ocellus. One pair of convergent vertical bristles. Antennae ( Fig. 5B) arising near middle of head; scape small, shorter than half length of pedicel; pedicel large elongate, with pair of ventroapical bristles; postpedicel spatulate, with dorsoapical arista­like style not longer than thorax; scape and pedicel dark brown, postpedicel and style yellowish­brown. Palpus elongate with long, distinct apical bristle.

Thorax. Ground colour yellowish­brown to dark. Postpronotal lobe small, with 2 pprn; acr biserial; 2 npl and several additional hairs, dc biserial; 2 spal; 1 pal; 1 subapical pair of sctl, less than one­half length of apical sctl; 1 apical pair of sctl long and slightly convergent. Tomentum pattern of scutum not visible.

Wing. ( Fig. 5C) Length 1.3 mm. Broad with blunt­tip; hyaline; microtrichia evenly distributed; costal setulae well developed; R extending to apical third of wing; R 4+5 parallel to M 1+2, only slightly curved toward costa; cell br much shorter than cell bm; crossvein bm­cu nearly transverse; A 1 only slightly visible as a fold. Knob of halter slightly elongated and yellowish­brown.

2+3

Legs. Fore femur well swollen in comparison to mid and hind femora, with row of prominent lengthened posteroventral bristles; fore tibia without prominent preapical ventral bristle. Mid femur less swollen than foreleg, with row of 4–5 outstanding posteroventral bristles about 1.5x as long as width of femur ( Fig. 5C); apical fourth with long anterior preapical bristle similar to posteroventral bristles; mid tibia without outstanding bristles. Hind femur slightly bent near base, with row of short anteroventral bristles. Hind tibia with erect dorsal and ventral bristles on apical half.

Abdomen. Segments elongate, uniformly telescopic, lacking distinctive bristles. Terminalia: Sternite 8 elongate, subequal to preceding sternite; sternite 8 with apex not partially separated from base. Tergite 10 absent; sternite 10 positioned below cerci. Cercus about one­third length of sternite 8, with several outstanding lateral and preapical bristles.

TYPE. Holotype female from Mexico: exact locality unknown, MX 395 — H. Deposited in SMNS. The holotype is in a somewhat cube­shaped piece of yellowish amber measuring about 3 x 2.5 mm.

REMARKS. The inclusion represents the first fossil species of Stilpon to be described and was originally found together with two specimens of Phoridae (Diptera) and one homopteran. Besides the features mentioned in the diagnosis, the thorax of this species appears a little more elongate in comparison to other members of the genus, however the thorax is damaged.

Extant species of Stilpon occur in low­lying vegetation zones of various open habitats, such as grasslands, sandy coastal areas, sedge and moss habitats of marshes and bogs, and low understudy vegetation and humus in open riparian woodlands ( Cumming & Cooper 1992).

ETYMOLOGY. The specific epithet refers to the Mexican origin of the amber harbouring this species.