PROC. BIOL. SOC. WASH. 98(4), 1985, pp. 1035-1041 A NEW BURROWING CRAYFISH (DECAPODA: CAMBARIDAE) FROM SOUTHWESTERN ARKANSAS Horton H. Hobbs, Jr. and Henry W. Robison Abstract.— Fallicambarus (F.) harpi, a burrowing crayfish, is described from two localities in the Caddo River (a tributary of the Ouachita River) basin of Pike County, Arkansas. It differs conspicuously from its closest relatives, F. (F.) strawni (Reimer, 1 966) and F. (F.)jeanae Hobbs (1973), in possessing a free (never adnate) cephalic process on the first pleopod of the first form male. The new crayfish described here is the fourth member of the nominate subgenus of Fallicambarus to be reported from Pike County, Arkansas: F. (F.) strawni (Reimer, 1966) occurs in the extreme western part of the county, F. (F. spectrum Hobbs (1973) in the north-central part (both in the Little Missouri River basin), and F. (F.)jeanae Hobbs (1973) and F. (F.) harpi, new species, in the northeastern part of the county in the Antoine River basin and the Caddo River basin, re-spectively. Only two other crayfishes, F. (F.) macneesei (Black, 1967) and F. (F.) dissitus (Penn, 1955), which range to the south and southeast, exhibit character-istics ascribed to the typical subgenus (see Hobbs 1973:463). Fallicambarus {Fallicambarus) harpi, new species Fig. 1 Diagnosis. — Antennal scale reduced; ventral surface of propodus of chela lack-ing row of stiff setae along lateral margin, tubercles of 2 ventral rows on merus of cheliped small but distinct; mesial ramus of uropod lacking distolateral spine. First pleopod of first form male almost straight and bearing small or well developed caudodistally directed cephalic process; mesial process little curved and directed caudally, and central projection strongly arched with apex directed proximally. Telson with transverse suture. Coxa of fourth pereiopod of male with very strong, compressed boss with rounded ventral margin. Chela slightly more than half as wide as long, and length of mesial margin of palm less than half width of palm. Annulus ventralis as figured: not broadly excavate anteriorly and not obscuring sclerite immediately caudal to annulus. Holotypic male, form I. —Body subovate, somewhat compressed although bran-chiostegites somewhat inflated (Fig. la, k). Abdomen much narrower than ceph-alothorax (10.5 and 16.8 mm). Greatest width of carapace distinctly posterior to caudodorsal extremity of cervical groove and greater than height (16.8 and 15.1 mm). Aerola linear over much of its length which comprising 40.8 percent of entire length of carapace (45.6 percent of postorbital length). Rostrum with convergent, moderately thickened margins, contracting anteriorly forming short triangular acumen, apex of which corneous, slightly upturned, and extending just beyond base of penultimate podomere of antennular peduncle. Dorsal surface of rostrum
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