SYSTEMATICS OF THE NEW-WORLD RACHISPODA LIOY (DIPTERA, SPHAEROCERIDAE) - MORPHOLOGY, KEY TO SPECIES GROUPS, AND REVISIONS OF THE ATRA, FUSCIPENNIS, LIMOSA AND VESPERTINA SPECIES GROUPS

The subgenus Leptocera (Rachispoda) is elevated to generic status and a key to the New World species groups of Rachispoda is given. The New World fauna comprises 13 species groups: the primarily Nearctic atra, cryptica, fumipennis, fuscipennis, limosa, lutosa and vespertina group s; and the primarily Neotropical aequipilosa, divergens, fuscinervis, maculinea, marginalis, and m-nigrum groups. The New World species of t he atra, fuscipennis, limosa, and vespertina species groups are revise d. The atra group comprises 12 New World species: R. arnaudi sp. nov.; R. atra (Adams) comb, nov.; R. canadensis sp. nov.; R. digitata sp. n ov.; R. eurystyla sp. nov.; R. falcicula sp. nov.; R. mexicana sp. nov .; R. pectinata sp. nov.; R. pereger sp. nov.; R. rhizophora sp. nov.; R. subsolana sp. nov.; and R. subulata sp. nov. The fuscipennis group is represented in the New World only by the widespread species R. fusc ipennis (Haliday) comb. nov. The limosa group comprises 5 species in t he Nearctic region: R. anathema sp. nov.; R. cryptistyla sp. nov.; R. frosti (Johnson) comb. nov.; R. hoplites (Spuler) comb. nov.; and R. l imosa (Fallen). The vespertina group comprises 3 Nearctic species: R. lacustrina sp. nov.; R. spatulata sp. nov.; and R. vespertina sp, nov. A lectotype is designated for Limosina setigera Adams (= R. atra). Le ptocera echinaspis Spuler is synonymized with R. fuscipennis (Haliday) . Postabdominal structure in the Sphaeroceridae is reviewed and a revi sed system of terms adopted in an effort to arrive at a standardized i nterpretation for the male and female postabdomen of Rachispoda that i s in agreement with new interpretations in the Diptera and applicable across the order. The terms are consistent with a revised version of H ennig's epandrial hypothesis on the origin of the male terminalia. The competing periandrial hypothesis of Griffiths is not supported by mor phological characters.