1	Cuticle translucent to white. Eyes absent. Antenna with antennomere V much wider than the other antennomeres (Figure 1C). Associated with ants. (Platyarthridae)	Platyarthrushoffmannseggii Brandt, 1833
–	Cuticle color variable. Eyes present, each usually compound or with one or three ocelli. Antenna variable, but antennomere V not significantly wider than the others. Not associated with ants or associated with ants only incidentally	2
2	Antennal flagellum comprising two to many distinct articles (Figs 1D, 3E, 4A, B, 5A, B, F, G)	3
–	Antennal flagellum superficially appearing to be one article, either robust (fl, Figure 1E) or thin, tapering and elongate (Figure 2A–C), but comprising up to six articles visible with high magnification	4
3	Antenna with two distinct flagellar articles (Figs 3E, 4A, B). Uropods may extend beyond elliptical perimeter of the body in dorsal view (Figure 4A, B) or may not (Figure 3B, D)	9
–	Antenna with three distinct flagellar articles (Figure 5A, B). Uropods extending beyond elliptical perimeter of body in dorsal view; protopodite usually not extending beyond pleotelson; exopodite large, conical or spear-head shaped; endopodite thin (Figure 5A, B, D)	16
–	Antenna with four distinct flagellar articles (Figure 1D). Uropods completing posterior elliptical perimeter of body in dorsal view, protopodite large, dorsoventrally flattened; exopodite small, endopodite elongate (Figure 1D). (Detonidae)	Armadilloniscusellipticus (Harger, 1878)
–	Antenna with flagellum long, comprising 10 or more flagellar articles (Figure 5F, G). Uropods extending beyond elliptical perimeter of body in dorsal view; with protopodite robust, projecting posteriorly beyond pleotelson; endopodite and exopodite thin, elongate (Figure 5F, G). (Ligiidae)	19
4	Compound eye present. Antennal flagellum approx. the same width basally as antennomere V and comprising four articles that decrease in size distally (fl, Figure 1E). Sandy marine beaches. (Scyphacidae)	Scyphacellaarenicola Smith, 1873
–	Compound eye absent, but with one or three ocelli. Antennal flagellum abruptly narrower than preceding article, a narrow tapering cone (Figure 2A–C) comprising up to six articles visible with high magnification. Not usually associated with sandy marine beaches. (Trichoniscidae)	5
5	Surface of pereon smooth; without tubercles, denticles or other sculpture (Figure 2A)	6
–	Surface of pereon sculptured, with tubercles and/or denticles (Figure 2B, C)	7
6	Each eye with three ocelli. Antenna with four or five flagellar articles visible with high magnification. Body length up to 5 mm (Figure 2A)	Trichoniscuspusillus Brandt, 1833
–	Each eye with one ocellus. Antenna with six flagellar articles visible with high magnification. Body similar to Figure 2A, length up to 7 mm	Hyloniscusriparius (C. L. Koch, 1838)
7	Pereon with tubercles or denticles on longitudinal ridges (Figure 2B). Pleon not abruptly narrower than pereon; pleonal tergites with prominent epimera. Cuticle translucent or white, without dark pigments. Antenna with three flagellar articles visible with high magnification	Haplophthalmusdanicus Budde-Lund, 1880
–	Pereon with tubercles in transverse or roughly transverse rows (Figure 2C). Pleon abruptly narrower than pereon. Cuticle pigmented. Antenna with four flagellar articles visible with high magnification. (Miktoniscus)	8
8	Male pleopod I (Figure 2D) with exopodite long, almost as long as endopodite, ending in point; tip of endopodite long, round in cross section. Near marine or estuarine grasses, debris, etc. but may also occur in moist inland habitats	Miktoniscusspinosus (Say, 1818)
–	Male pleopod I (Figure 2F) with exopodite shorter, approx. half the length of endopodite, tapering distally but terminus broadly rounded; endopodite long, flattened in cross section. Moist terrestrial habitats	Miktoniscusmedcofi (Van Name, 1940)
9	Exopodite of uropod not extending beyond elliptical perimeter of body in dorsal view; broad, dorsoventrally flattened; protopodite and endopodite largely hidden in dorsal view (Figure 3B, D, E, cf. 1B). In life, able to roll into a ball with antennae hidden. (Armadillidiidae: Armadillidium)	10
–	Exopodite of uropod extending beyond elliptical perimeter of body in dorsal view; protopodite visible in dorsal view; exopodite prominent, attaching at terminus of protopodite, broad basally, tapering distally; endopodite thin, attaching at medial base of protopodite (Figure 4A, B). In life, unable to roll into a ball or, if able to enroll, antennae remain exposed	11
10	Head with median frontal projection extending dorsally, with dorsal margin overlapping anterior edge of cephalic dorsum (fp, Figure 3A). Pleotelson subtrapezoidal, with posterior margin nearly straight (pt, Figure 3B)	Armadillidiumvulgare (Latreille, 1804)
–	Head with prominent, median frontal projection extending dorsoanteriorly and not overlapping anterior edge of cephalic dorsum (fp, Figure 3C). Pleotelson subtriangular with posterior apex variably produced, but typically with rounded terminus (pt, Figure 3D)	Armadillidiumnasatum Budde-Lund, 1885
11	Pleon abruptly narrower than pereon (Figure 4B). Anterolateral lobes very small. Cuticle often with frosted-gray or dusty appearance, but this may be absent. Antennomeres IV and V usually with white terminal band. Frontal margin without evident median projection. (Porcellionidae, in part)	Porcellionidespruinosus (Brandt, 1833)
–	Pleon not abruptly narrower than pereon (Figure 4A). Anterolateral lobes prominent (Figure 4A, C–F). Cuticle without frosted-gray appearance. Antenna color variable but antennomeres IV and V usually without terminal white bands. Frontal margin with some form of median projection (Figure 4A, C–F)	12
12	Dorsal surface of pereon essentially smooth	13
–	Dorsal surface of pereon with numerous bumps or tubercles	14
13	Posterolateral margin of first pereonal tergite produced posteriorly into pointed angle (arrow, Figure 4F). Five pairs of lungs present. Frontal margin of head with small median triangular projection (Figure 4F) corresponding to vertical median carina of frontal lamina (ca, Figure 1A). In life, capable of rolling into a ball with antennae exposed. (Cylisticidae)	Cylisticusconvexus (De Geer, 1778)
–	Posterolateral angle of first pereonal tergite bluntly rounded, not produced posteriorly into a pointed angle (arrow, Figure 4E). Lungs restricted to pleopods I and II. Frontal margin with broad, convex median projection (Figure 4E). In life, not capable of rolling into a ball. (Porcellionidae, in part)	Porcelliolaevis Latreille, 1804
14	Anterolateral lobes very prominent and broad, width of each approx. one-third width of head; in dorsal view, junction between median projection and anterolateral lobes V-shaped or nearly so (Figure 4C). Head dark brown to black, contrasting with base color of pereon. Pereon with dark mid-dorsal stripe (sometimes broken), usually bordered laterally by bright yellow markings that may be lost in preservative. (Porcellionidae, in part)	Porcelliospinicornis Say, 1818
–	Anterolateral lobes not so wide, joining convex median projection via curved margin, not V-shaped notches (Figure 4A, D). Head color not usually contrasting with base color of pereon. Pereon with dorsal color variable; if dark median line present, then not bordered by bright yellow markings	15
15	Five pairs of lungs. Dorsum of pereon with low, irregular bumps and tubercles; surface usually with pattern of dark brown, reddish brown and tan; lateral surface at base of epimera with tan to nearly-white patches creating a pair of broken lines. Frontal margin with broad convex median projection (Figure 4D). (Trachelipodidae)	Trachelipusrathkii (Brandt, 1833)
–	Lungs restricted to pleopods I and II (as in Figure 1B). Dorsum of pereon tuberculate; color variable, ranging from solid brown or gray to various patterns, sometimes similar to Trachelipus but usually without a pair of broken light lines at base of epimera. Frontal margin with prominent triangular to subtrangular median projection with rounded apex (Figure 4A). (Porcellionidae, in part)	Porcellioscaber Latreille, 1804
16	Head with prominent anterolateral lobes. Pleon not abruptly narrower than pereon, body broad and distinctly elliptical in dorsal view (Figure 5A). (Oniscidae)	Oniscusasellus Linnaeus, 1758
–	Head without anterolateral lobes. Pleon abruptly narrower than pereon, body more elongate, oblong in dorsal view (Figure 5B).	17
17	Found in vegetation or under objects near marine or brackish water. Pleotelson with lateral margins weakly concave, posterior apex bluntly rounded to truncate (pt, Figure 5E). Head with color similar to that of pereon; pereon often with dark mid-dorsal line bordered laterally by bright yellow splotches. (Halophilosciidae)	Littorophilosciavittata (Say, 1818)
–	Found in terrestrial environments. Pleotelson with lateral margins essentially straight (pt, Figure 5D) or distinctly concave (pt, Figure 5C). Coloration differing from above. (Philosciidae)	18
18	Pleotelson triangular, with lateral margins straight or nearly so in dorsal view, posterior apex blunt (pt, Figure 5D). Pleon rather elongate, sides straight in dorsal view, epimera not forming lateral serration. Dorsal coloration of pereon purple-brown with small, light longitudinal markings (lineoles), typically without distinct mid-dorsal stripe; head color similar to pereon. Thus far known in Maryland only from forests in Baltimore	Chaetophilosciasicula Verhoeff, 1908
–	Pleotelson with lateral margins distinctly concave, posterior apex pointed (pt, Figure 5B,C). Pleon more compact, epimera giving sides a serrate appearance in dorsal view. Dorsal coloration of pereon highly variable, but often brown with pattern of lighter markings, usually with very dark mid-dorsal line; head dark brown to black, often contrasting with lighter pereon. Widespread. (Philosciidae)	Philosciamuscorum (Scopoli, 1763)
19	Uropod with protopodite very long, surpassing posterior terminus of pleotelson by more than the length of pleotelson; endopodite and exopodite long and thin, about equal in length, both arising from tip of protopodite (Figure 5F). Marine or brackish shorelines, splash zone, and directly adjacent areas. Larger, up to 4.8 cm	Ligiaexotica Roux, 1828
–	Uropod with protopodite exceeding posterior tip of pleotelson by about one length of the pleotelson or less; endopodite about 1.5 times the length of exopodite, endopodite arising from protopodite proximal to exopodite (Figure 5G). Wet litter in woodlands, wetlands, near streams, etc. in mountains. Smaller, up to 1 cm	Ligidiumelrodii (Packard, 1873)