1	Outer subhumeral stria subcarinate to strongly carinate, forming a lateral elytral margin of varying strength (Fig. 80A) (where weak, in one species from Central Mexico (Fig. 80G), the epistoma has weak oblique lateral striae); lateral submarginal pronotal stria complete, carinate, very close to margin, pronotal disk depressed along its inner edge (Fig. 80C); body otherwise highly varied in appearance, often strongly carinate (Fig. 80A), or conversely with striae strongly reduced (Fig. 82E); never strongly and densely punctate	Operclipygus marginellus group (p. 315)
–	Outer subhumeral stria variously impressed, but rarely carinate; if elytra with lateral carina, then body is densely and uniformly punctate throughout; lateral submarginal pronotal stria, if close to margin, rarely carinate, and pronotal disk not depressed along its inner edge	2
2	Pronotum with a single pair of anterior gland openings, located along pronotal margin behind eye	3
–	Pronotum with two pairs of anterior gland openings, at least one along the anterior margin laterad eye, the second, median opening variable in position, may be close to anterolateral opening or displaced posterad on pronotal disk by as much as three-fourths the pronotal length	4
3	Body size <3 mm; pronotum with strong basal plicae; frontal striae abruptly bent dorsad near antennal bases, sinuate across middle (Fig. 8F); known only from a cave near Tingo Maria, Huanuco, Peru	Operclipygus schlingeri sp. n.
–	Body large, >5 mm, subquadrate (Fig. 103); pronotum lacking basal plicae; southeastern Brazil	Operclipygus iheringi (Bickhardt)
4	Median pronotal gland openings close to anterior pronotal margin, within approximately 10 diameters (Figs 5A, B)	5
–	Distance between median pronotal gland openings and anterior pronotal margin greater than, usually much greater than, 10 diameters (Fig. 5C); or, pronotal disk strongly and uniformly punctate, obscuring gland openings	41
5	Anterior submarginal pronotal stria continuous with lateral submarginal stria, joined smoothly, without postocular angulation; both pronotal gland openings very close to anterior margin (Fig. 5A), anterior to submarginal stria, median openings no more than two diameters from anterior margin	Operclipygus farctus group (p. 182)
–	Anterior submarginal pronotal stria detached from lateral submarginal stria, or meeting at distinct postocular angulation; median pronotal gland openings ranging from 4-10 diameters from anterior pronotal margin	6
6	Distinct pronotal plicae present (Fig. 5E)	7
–	Pronotal plicae absent, pronotum at most weakly flattened across base	8
7	Frons flat to convex, with frontal stria complete, transverse; body not unusually large	Operclipygus mirabilis group (females) (p. 39)
–	Frons strongly impressed at middle (Fig. 22A), frontal stria sinuate laterally or interrupted over antennal bases; body large, rounded, strongly convex	Operclipygus mortavis group (p. 91)
8	Metaventrite and first abdominal ventrite with coarse punctures (Figs 6C, 19B); second lateral metaventral stria present laterad primary stria; elytra usually with numerous poorly organized punctures toward apex (Fig. 5F)	Operclipygus sejunctus group (p. 77)
–	Metaventrite (and usually first abdominal ventrite) lacking coarse punctures; other characters variable	9
9	Body elongate, parallel-sided (Fig. 7A); prosternal lobe large, subtruncate apically (Fig. 7F); both mandibles with strong basal tooth (Fig. 4E); secondary lateral metaventral stria present	Operclipygus sulcistrius group (p. 34)
–	Body form varied; left mandible usually without, or with only small tooth; prosternal lobe rounded, never subtruncate apically; secondary lateral metaventral stria rarely present	10
10	Body small (usually <2mm), usually elongate, more or less parallel-sided; 1st abdominal ventrite with two complete lateral striae, usually well separated (Figs 30C, 34A); prescutellar impression present, narrow, elongate	11
–	Body usually larger, rounded or elongate; 1st abdominal ventrite with one or two lateral stria, but rarely with both complete – if two present then close together near metacoxa; prescutellar impression varied, but rarely thin and elongate	12
11	Left mandible with small but distinct basal tooth (Fig. 30A); antennal club large, circular; anterior mesoventral emargination deep, nearly meeting arch of mesometaventral stria (Fig. 30C); lateral metaventral stria approximately longitudinal, directed at inner half of metacoxa; pygidium short, wider than long (Fig. 30D); male genitalia generally short, with broad aedeagus bearing strong medioventral tooth (Figs 31–33)	Operclipygus dubius group (p. 113)
–	Left mandible usually lacking tooth, or with minute denticle; antennal club smaller, more elongate; mesoventral emargination varied; lateral metaventral stria more oblique, extending toward middle or outer third of metacoxa; pygidium generally longer; male genitalia varied, but never as above	Operclipygus hospes group (p. 129)
12	Body small (~2mm), rounded; marginal pygidial sulcus deep, strongly crenulate on inner edge (Figs 15B–D); outer subhumeral stria short, present only apically	Operclipygus impuncticollis group (p. 64)
–	Marginal pygidial sulcus rarely strongly crenulate on inner edge (may be absent); other characters varied	13
13	Frons convex, not at all depressed at middle (Fig. 11B); central portion of frontal stria detached from sides, not strongly impressed; inner and outer subhumeral striae complete; pygidium with dense, fine ground punctation (with or without coarser secondary punctures)	Operclipygus kerga group (p. 52)
–	Frons at least weakly depressed in middle; other characters variable, but very rarely with both subhumeral striae complete	14
14	Epistoma, prosternal lobe, prosternal keel, mesoventral disk with dense ground punctation (often other body surfaces as well, esp. pronotum, frons, metaventrite; Fig. 13); central portion of frontal stria absent; elytron with fine series of apical punctures	Operclipygus conquisitus group (p. 57)
–	Epistoma and prosternal lobe lacking dense ground punctation; central portion of frontal stria usually present (may be detached and/or interrupted); apex of elytra rarely with fine series of apical punctures	15
15	Central portion of anterior pronotal margin outwardly arcuate or angulate	16
–	Central portion of anterior pronotal margin not produced	20
16	Frons very strongly depressed at middle (Figs 28C, E); central portion of anterior pronotal margin strongly angulate at middle; base of prosternal keel weakly emarginate	Operclipygus impressifrons group (p. 106)
–	Frons not so strongly depressed at middle; central portion of anterior pronotal margin more weakly angulate or arcuate; base of prosternal keel varied, rarely weakly emarginate	17
17	Frontal stria complete, central portion connected to sides; pygidial sulcus finely impressed, may be abbreviated basally	18
–	Frontal stria interrupted at sides, central portion detached; pygidial sulcus strongly impressed, crenulate	Operclipygus panamensis (Wenzel & Dybas)
18	Outer subhumeral stria complete, inner absent; abdominal ventrites 3 and 4 with single series of large deep punctures (Fig. 85G); propygidium with dense medial grouping of small but deep punctures (Fig. 85H), with more or less impunctate band along basal and lateral margins; marginal pygidial sulcus complete	Operclipygus lama Mazur
–	Outer subhumeral stria not complete, interrupted at middle or present only in apical half; abdominal ventrites 3 and 4 with more numerous smaller punctures not forming a single series; marginal pygidial sulcus obsolete basally	19
19	Lateral submarginal pronotal stria absent from basal half; outer subhumeral elytral stria present only in apical half; inner subhumeral stria absent; body form strongly narrowed, sides subparallel (Fig. 95C)	Operclipygus brooksi sp. n.
–	Lateral submarginal pronotal stria complete along side; outer subhumeral stria reaching base and apex, but interrupted at middle; fragments of inner subhumeral stria generally present; body moderately narrowed, but sides weakly rounded (Fig. 95A)	Operclipygus peregrinus sp. n.
20	Coarse punctures of propygidium discretely limited to central part of disk (though fine series may also be present along extreme lateral margin; Figs 95E, 98E); sides of propygidium with only dense, fine ground punctation	21
–	Propygidium with coarser secondary punctures more or less uniformly distributed	23
21	Outer subhumeral stria present only in apical half; body shape distinctly rounded (Fig. 95D)	Operclipygus profundipygus sp. n.
–	Outer subhumeral stria complete; body shape subcylindrical, with sides narrow and subparallel (Fig. 98D)	22
22	5th dorsal elytral stria present in apical half and represented by a distinct basal puncture (Fig. 98D); marginal pronotal bead weakly widening toward the front; apex of aedeagus lacking ventrolateral processes	Operclipygus parallelus sp. n.
–	5th dorsal elytral stria present in apical half only, lacking basal puncture; marginal pronotal bead widening toward the front; apex of aedeagus with thin, membranous, ventrolateral processes (Fig. 99E)	Operclipygus siluriformis sp. n.
23	Elytra coarsely punctate, partially obliterating otherwise mostly complete elytral striae, particularly the apices of 4th and 5th striae (Fig. 85C); ground punctation of pronotum very conspicuous, but coarse secondary pronotal punctures limited to sides; frontal stria complete, transverse; pygidium with fine ground punctation and dense secondary punctation; marginal pygidial sulcus deeply impressed, complete (Fig. 85E)	Operclipygus punctulatus sp. n.
–	Elytra not coarsely punctate, except rarely along apical margin; other characters variable	24
24	Outer subhumeral stria complete	25
–	Outer subhumeral stria abbreviated, interrupted, or absent	32
25	Inner subhumeral stria complete	Operclipygus cavisternus sp. n.
–	Inner subhumeral stra abbreviated or absent	26
26	Marginal pygidial stria fragmented, abbreviated, or absent	27
–	Marginal pygidial stria complete, well impressed	28
27	4th dorsal elytral stria abbreviated; pygidium with dense ground punctation, lacking coarse secondary punctures (Fig. 101D)	Operclipygus faltistrius sp. n.
–	4th dorsal stria complete; pygidium with only sparse ground punctation, with or without secondary punctures	Operclipygus teapensis (Marseul)
28	Pronotum with numerous, conspicuous coarse punctures at sides (Fig. 88A); abdominal ventrites 3 and 4 with primary series of large, deep punctures, with few smaller punctures intermingled	Operclipygus florifaunensis sp. n.
–	Pronotum lacking coarse lateral punctures; abdominal ventrites 3 and 4 without single dominant series of large deep punctures	.29
29	Elytron with two complete and one partial epipleural striae; pronotal marginal bead wide, convex (Fig. 91A); body larger, ~3.5 mm	Operclipygus arnaudi Dégallier
–	Elytron with one complete epipleural stria (often a second, incomplete); pronotal marginal bead varied, weakly convex; body smaller, ~2–3mm	30
30	Elytron with single epipleural stria, with wide smooth epipleuron below; 4th dorsal elytral stria abbreviated from base	31
–	Elytron with one complete upper epipleural stria, and an abbreviated lower stria; 4th dorsal elytral stria complete	Operclipygus rupicolus sp. n.
31	Punctures of propygidium small, deep, and rather dense; marginal pygidial sulcus very deep and strongly crenulate (Fig. 101B); South America	Operclipygus pygidialis (Lewis)
–	Punctures of propygidium rather large, shallow, and sparse (Fig. 101F); marginal pygidial sulcus deep, but narrower and only weakly crenulate; known from Costa Rica	Operclipygus limonensis sp. n.
32	Marginal pygidial sulcus absent (rarely with few weak apical fragments present)	33
–	Marginal pygidial sulcus present, generally well impressed and complete	34
33	Pygidium with dense, fine ground punctation only, lacking any coarser punctures (Fig. 95G); lateral submarginal pronotal stria complete; pronotum lacking coarse lateral punctures; punctures of propygidium small, concentrated in basal two-thirds	Operclipygus punctatissimus sp. n.
–	Pygidium with dense, fine ground punctation and markedly coarser punctures uniformly interspersed (Fig. 101H); lateral submarginal pronotal stria obsolete in basal half; pronotum with numerous coarse lateral punctures very close to lateral margin (Fig. 101G)	Operclipygus wenzeli sp. n.
34	Lateral submarginal pronotal stria obsolete in basal half	35
–	Lateral submarginal pronotal stria complete along side	36
35	Elytral epipleuron elevated, flat below strong subhumeral swelling, with numerous coarse punctures on side in anterior half (Fig. 92F); outer subhumeral stria present in apical half only	Operclipygus punctipleurus sp. n.
–	Elytral epipleuron normally rounded, subhumeral region less strongly swollen, lacking coarse punctures; outer subhumeral stria present in apical half and as isolated basal fragment	Operclipygus falini sp. n.
36	Marginal pygidial stria strongly impressed, diverging from margin toward apex (Fig. 91G); pronotum with linear prescutellar impression about equal in length to scutellum	Operclipygus latipygus sp. n.
–	Marginal pygidial stria following margin throughout, marginal bead uniform in width; prescutellar impression varied (may be absent)	37
37	Body small, ~1.5 mm, broadly rounded (Fig. 91C); lateral metaventral stria curving laterad toward metepisternum	Operclipygus subsphaericus sp. n.
–	Body larger, >2 mm, more distinctly elongate oval; lateral metaventral stria extending posterad toward metacoxa	38
38	Elytron with 4 complete dorsal striae, with only one complete (and possibly additional abbreviated) epipleural stria	40
–	Elytron with 4th dorsal stria abbreviated from base, present in apical half only	39
39	Base of prosternal keel truncate (Fig. 88A); pygidial sulcus fine, complete (Fig. 88D); vestige of inner subhumeral stria generally present; body rounded (Fig. 88C)	Operclipygus bosquesecus sp. n.
–	Base of prosternal keel outwardly produced; pygidial sulcus weak, obsolete at base (Fig. 98H); inner subhumeral stria absent; body more elongate (Fig. 98F)	Operclipygus abbreviatus sp. n.
40	Body large, ~4 mm, piceous; frontal stria distinctly interrupted above antennal bases (and often also at middle); pygidium with both dense ground punctation and very dense secondary punctation (Fig. 17D)	Operclipygus crenatus (Lewis)
–	Body smaller, rufescent; frontal stria complete or very narrowly interrupted over antennal base; pygidium with dense, fine ground punctation with coarser punctures very sparsely intermingled (Fig. 92B)	Operclipygus elongatus sp. n.
41	Median pronotal gland openings associated with elaborations of pronotal striae, including anterolateral tubercles and shallow, sinuate channels (Fig. 9); pronotum usually with basal plicae; elytral apices with disorganized punctures, 4th and 5th elytral striae often obscured apically; frons flat to convex, frontal stria complete, transverse; lateral submarginal striae rarely extending inward along anterior margin from corners	Operclipygus mirabilisgroup (males) (p. 39)
–	Median pronotal gland openings never associated with secondary sexual modifications, generally simple in both sexes; elytral apices with or without apical punctures, but 4th and 5th dorsal striae rarely both abbreviated apically	42
42	Pronotal plicae present; head disproportionately large (Fig. 62C); mandibles prolonged at apices (Figs 62E–G)	Operclipygus plicicollis group (p. 249)
–	Pronotal plicae absent	43
43	Body large (>7mm), strongly convex; legs broadly expanded, the meso- and metathoracic legs about two-thirds as wide as long (Fig. 80E); only known from Minas Gerais, Brazil	Operclipygus formicatus sp. n.
–	Body smaller, convex or not; legs elongate, no more than one-third as wide as long	44
44	Median pronotal gland openings obscured by dense pronotal punctation (Figs 24A, D, E); prosternal lobe elevated along midline (Fig. 24B); body generally conspicuously and completely punctate, depressed, elongate; lateral submarginal pronotal stria close to margin, subcarinate, continuous with anterior submarginal stria	Operclipygus dytiscoides group (p. 96)
–	Median pronotal gland openings distinct, situated one-third or more pronotal length behind anterior margin; prosternal lobe not elevated along midline; other characters variable	45
45	Median pronotal gland openings at or just in front of pronotal midline (Figs 54B, D); ventral surface of tarsomeres with dense brush of setae, not in organized lateral series (Fig. 54A); 9th tergite of male genitalia with apices dorsolaterally flattened, divergent (Fig. 55C)	Operclipygus hirsutipes group (p. 213)
–	Median pronotal gland openings behind pronotal midline; ventral surface of tarsi with setae organized in distinct lateral rows; 9th tergite of male never with apices flattened and divergent	46
46	Mandibles strongly dentate (Fig. 45G); epistoma strongly convex; body elongate, parallel sided, subdepressed (Fig. 45F); anterior submarginal pronotal stria detached, strongly recurved posterad; median pronotal gland openings about two-thirds behind pronotal margin	Operclipygus bulbistoma sp. n.
–	Left mandible with at most a very weak tooth; epistoma flat to subdepressed; other characters varied	47
47	Base of prosternal keel weakly emarginate; pygidial sulcus weak, never complete and rarely absent; microsculpture generally present on propygidium (Fig. 6F, 56A), often also on pygidium, metaventrite, and 1st abdominal ventrite; anterior submarginal pronotal stria frequently detached from lateral stria (Fig. 56C); pygidium never with dense ground punctation; elytra always with 4 or more complete dorsal striae; body usually rufescent (Fig. 56D), rarely darker	Operclipygus hamistrius group (p. 218)
–	Base of prosternal keel subtruncate to posteriorly arcuate, rarely emarginate; pygidial sulcus varied from absent to strong, rarely weak and abbreviated; propygidium lacking microsculpture (microsculpture may be present on parts of the venter); anterior and lateral submarginal pronotal striae continuous across anterior margin, anterior portion rarely detached; pygidium frequently with dense, fine ground punctation; elytral striation frequently reduced; body color darker, generally rufopiceous	48
48	Anterior submarginal pronotal stria narrowly detached from lateral, barely recurved posterad at sides (Fig. 105A); anterior pronotal margin projecting at middle, with marginal stria complete along anterior edge; posterior half of lateral pronotal margin bent ventrad, nearly vertical; propygidium with dense ground punctation at sides, with coarse punctures more or less restricted to middle of propygidium; marginal pygidial sulcus complete, but not ending in basal foveae (Fig. 105C)	Operclipygus angustisternus (Wenzel & Dybas)
–	If anterior submarginal pronotal stria detached from lateral stria, then anterior pronotal margin not projecting; other characters varied	49
49	Outer subhumeral stria complete or interrupted at middle, present in basal and apical halves; pygidial marginal sulcus usually deep and coarse, often ending in basal foveae, though sulcus and/or foveae may be lacking	50
–	Outer subhumeral stria present in apical half only or absent; pygidial sulcus fine, without basal pygidial foveae	Operclipygus impunctipennis group (p. 277)
50	Pygidium with deep marginal sulcus widened in basal half, but not abruptly enlarged (Fig. 105E), basolateral foveae absent; 3rd dorsal elytral stria interrupted; aedeagus narrow and elongate, not short and broad, with very weak medioventral process; known only from Venezuela	Operclipygus shorti sp. n.
–	Pygidium with or without marginal sulcus, but sulcus never gradually widened in basal half; basolateral pygidial foveae present or absent; 3rd dorsal elytral stria complete; aedeagus short and broad (e.g., Fig. 65G), with strong medioventral process; median lobe with large gonopore frequently exposed beneath	Operclipygus fossipygus group (p. 256)