Jennifer Reaney and Douglas G. Pfeiffer

(1b) 2a. With a cribellum (a transverse mate) in front of the spinnerets, and a calamistrum (row of bristles) on metatarsus IV, varying from just a few bristles to a row the entire length of the metatarsus..........Section CRIBELLATAE 3
(1b) 2b. Without a cribellum and calamistrum..........Section ECRIBELLATAE 4

(2a) 3a. Tarsi with a dorsal row of trichobothria (long, five setae). Eight eyes all light in color..........Family AMAUROBIIDAE
(2a) 3b. Tarsi either without trichobothria, or at most with one. Eight eyes either all dark, or eyes heterogeneous, the anterior medians alone dark; or with only six eyes, the anterior medians lacking..........Family DICTYNIDAE

(2b) 4a. With two, four, or six eyes..........5
(2b) 4b. With eight eyes..........6

(4a) 5a. Tracheal spiracle (or spiracles) opening just behind the epigastric furrow..........Family SEGESTRIIDAE
(4a) 5b. Tracheal spiracle opening either just in front of spinnerets, or at about the middle of the venter..........Family AGELENIDAE

(4b) 6a. Tarsi with two claws, with or without claw tufts..........7
(4b) 6b. Tarsi with three claws, never with tufts, though spurious claws may be present..........12

(6a) 7a. Eyes in three or four rows..........Family SALTICIDAE
(6a) 7b. Eyes in the more common arrangement of two rows..........8

(7b) 8a. Tracheal spiracle in advance of the spinnerets at least one-third of the distance between the latter and epigastric furrow..........Family ANYPHAENIDAE
(7b) 8b. Tracheal spiracle in the usual place just in front of the spinnerets..........9

(8b) 9a. At least legs I and II laterigrade, i.e., turned so that the morphologically dorsal surface is posterior and the prolateral surface appears to be the dorsal..........10
(8b) 9b. All legs of the usual prograde type..........11

(9a) 10a. Colulus present (a small appendage resembling a tiny spinneret, located immediately anterior to spinnerets). Hair over body simple and erect. Legs I and II much longer and stouter than III and IV. Claw rufts lacking, or composed of simple hairs, and tarsi I and II not scopulate. Promargin of cheliceral fang furrow unarmed..........Family THOMISIDAE
(9a) 10b. Colulus absent. Hair over body feathery or scaly, and prone. All legs about the same length or leg II alone much longer. Claw tufts composed of spatulate hairs and tarsi I and II scopulate. Promargin with one or two teeth..........Family PHILODROMIDAE

(9b) 11a. Anterior spinnerets conical, contiguous or almost so, and not more heavily sclerotized than the posterior. Eyes homogeneous or almost so (with few exceptions). Endites (mouthparts ventral to mouth opening, opposing chelicerae) without a transverse or oblique depression (except in Micaria)...........Family CLUBIONIDAE
(9b) 11b. Anterior spinnerets cylindrical, longer and more heavily sclerotized than the posterior, and separated by a distance about equal to the diameter of one. Eyes distinctly heterogeneous, the anterior medians alone dark; the posterior medians often oblique, oval or triangular. Endites with an oblique depression (a) on the ventral face..........Family GNAPHOSIDAE

(6b) 12a. Eye group hexagonal, the posterior row procurved, the anterior row recurved, with the clypeus high. (Abdomen pointed behind and legs with very prominent spines..........Family OXYOPIDAE
(6b) 12b. Eye group not forming a hexagon, and clypeus much lower..........13

(12b) 13a. With tarsus IV in most specimens provided for at least one-sixth its length from the distal end with a ventral row of 6 to 10 serrated bristles, forming a comb, which may be poorly developed in males. Spiders hanging in an inverted position in irregular mesh webs..........Family THERIDIIDAE
(12b) 13b. Tarsus IV without such a comb..........14

(13b) 14a. Tarsi with trichobothria . Labium withuot thickened front margin..........15
(13b) 14b. Tarsi without trichobothria. Labium with a thickened font margin..........16

(14a) 15a. Posterior row of eyes so strongly recurved that it may be considered to form two rows. Median claw smooth or with a single tooth. Anterior piece of lorum rounded behind a fitting into a notch of the posterior piece. Egg sac carried attached to spinnerets and young carried on mother's back..........Family LYCOSIDAE
(14a) 15b. Posterior row of eyes not forming two distinct rows, but only slightly recurved. Median claw with two or three teeth. Egg sac held under cephalothorax; young not carried about by mother..........Family PISAURIDAE

(14b) 16a. Clypeus in most lower than height of the median ocular area. Eyes homogeneous. Chelicera with a boss (a smooth prominence at base of lateral angle of chelicera), though rudimentary in some. (For the most part weavers of orb webs)..........17
(14b) 16b. Clypeus usually as high as, or more commonly higher than, height of the median ocular area. Eyes heterogeneous. Chelicerae without a boss. The majority do not weave orb webs..........18

(16a) 17a. Epigastric furrow between lung slits procurved. Rudimentary boss on chelicerae. In most specimens the chelicerae are large and powerful. Femora with trichobothria ..........Family TETRAGNATHIDAE
(16a) 17b. Epigastric furrow nearly straight. Boss conspicuously present on chelicerae in most, though rudimentary in some. Femora without trichobothria, or if present then femur IV provided with a double fringe of hairs on the prolateral surface..........Family ARANEIDAE

(16b) 18a. Tibia of male pedipalp without apophyses (a thick process) (though the tibia may be dilated distally). Palp of female in most species with a claw at the end of the tarsus. Tibia IV in most species with two dorsal spines, or if only one spine is present then there is one short spine on metatarsi I and II..........Family LINYPHIIDAE
(16b) 18b. Tibia of male pedipalp in most species with at least one apophysis. Palp of female without a claw at end of tarsus. Tibia IV with a single dorsal spine or bristle, and with the metatarsi spineless, or all spines lacking altogether..........Family MICRYPHANTIDAE