The morphological and other terms used here are, for the most part, those traditional to ant systematics. The worker caste of ants, a specialized female form, because of its structural modifications often presents some problems to the uninitiated.
     The explanations given below will, we hope, reduce possible confusion.

     Glossary of Descriptive Terminology

Acidopore - in formicine ants only, the circular, somewhat nozzle-shaped exit of the poison gland, formed by the last gastral sternite and usually surrounded by a distinct fringe of hairs (Fig. 0).
Acuminate - tapering to a fine, sharp apex or point.
Alate - with wings.
Alitrunk - see mesosoma.
Antennal fossa - the cavity or depression within which the antennal socket is situated.
Apical - the terminal or last segment of a structure.
Appressed - refers to a hair that is parallel to, or nearly parallel to, the body surface (Fig. 0).
Apterous - without wings.
Arboreal - nesting and living entirely in trees or shrubs.
Basad - located toward the base of a structure.
Basal - the first, or nearest the body, segment or portion of a structure.
Basitarsus - the first, or basalmost, tarsal segment (Fig. 0).
Bidentate - having two teeth, as in the paired teeth of the clypeal margin of Solenopsis (Fig. 00).
Carina - an elevated ridge on the body surface.
Carinate - with one or more carinae.
Cephalic Index (CI) - The ratio of head length to head width, as expressed in the formula: (HL/HW)(100).
Clavate - thickened or broadened toward the apex, i. e., more or less club-shaped.
Connules - the lateral, more or less cone-shaped projections of the postpetiole in the queens and major workers of some species of Pheidole (Fig. 00).
Cordate - heart-shaped.
Coxa - the basalmost leg segment.
Dealate - no longer possessing wings that formerly were present; this term is limited to female or queen ants or to both sexual forms of termites.
Declivity - a downward-sloping surface, such as the posterior surface of the propodeum as seen in profile.
Decumbent - referring to hairs inclined at 10°- 40° from the body surface (Fig. 0).
Dentate - possessing teeth or tooth-like projections.
Denticulate - possessing minute teeth or tooth-like projections.
Dimorphic - possessing two morphologically distinct worker subcastes, as in the genus Pheidole (Figs. 00, 00).
Disc - the central area of a particular structure or body region.
Distad - located at, or toward, the distal or farthest end of a structure.
Dorsal - referring to the dorsum, or upper surface, of a structure.
Dufour's gland - An exocrine gland that empties at the base of the sting.
Emarginate - with a shallow notch seemingly cut from the margin of a structure; see Excised.
Epigeic - living or at least foraging largely or entirely on the surface of the ground, as oppossed to Arboreal or Hypogeic.
Epinotum - see Propodeum.
Erect - referring to a hair that is perpendicular, or nearly so, to the body surface (Fig. 0).
Eye Length - The maximum diameter of the eye as measured in lateral view (Fig. 0, EL).
Excised - With a deep cut or notch; see Emarginate.
Falcate - sickle- or saber-shaped.
Femur - the third segment of the leg.Flagellum - the combined third and following antennal segments; see Funiculus and Pedicel.
Fossa - a large deep pit on the body.
Fovea - a pit on the body surface, often either elongate or irregular in shape.
Foveate - refers to a surface possessing foveae.
Frons - that area of the front of the head lying below the vertex but not including the interantennal area (Fig. 0).
Frontal triangle - a small, usually shiny and abruptly depressed triangular area adjacent to the basal margin of the clypeus (Fig. 0).
Funiculus - all antennal segments beyond the scape; includes both the Flagellum and Pedicel, q. v.
Gaster - that portion of the ant metasoma distad to the Petiole or petiole + Postpetiole; commonly also called the "abdomen".
Gastral - refers to the gaster; the term "gastric" is synonymous.
Gena - That portion of the side of the head lying behind the compound eye whenviewed in profile; not the area between the compound eye and the antennal insertion as defined by Hölldobler and Wilson (1990). The definition used here is consistent with that employed in other groups of aculeate Hymenoptera.
Glabrous - refers to a body surface that is hairless and often smooth and shiny as well. This definition is not equivalent to that of Hölldobler and Wilson (1990), who have accepted the often used, but incorrect, interpretation which does not include hairlessness.
Gaster - that portion of the Metasoma lying posterior to the Petiole or Petiole + Postpetiole. See Metasoma, Petiole, Postpetiole.
Gula - see Hypostomal area.
Gular teeth - see Hypostomal teeth.
Head - the prosoma or first body segment. We consider the head to be functionally hypognathous; therefore for descriptive purposes the Vertex is at the top of the head and the Mandibles are at the bottom, or ventral, portion, with the antennae placed on the front of the head.
Head Length - the maximum length of the head, from the lower clypeal margin to the summit of the vertex, not including the mandibles (Fig. 0, HL).
Head Width - the maximum width of the head, in frontal view, exclusive of the compound eyes (Fig. 0, HW).
Humerus - the "shoulder" or anterolateral corner of the pronotum; may also be referred to as humeral angle.
Hypogeic - living largely or entirely underground.
Hypostomal area - the central part of the posterior surface of the head, above the mouthparts (Fig. 0).
Hypostomal teeth - present in major workers and females of Pheidole; one or two pair, situated behind the mandibles on the lateral segment of the hypostomal suture.
Incrassate - conspicuously swollen toward the tip or apex.
Lamella - a thin, plate-like process.
Major worker - a member of the largest worker subcaste, often morphologically distinct from the other subcastes and with different functions; see Media worker and Minor worker.
Malar area - with the head in lateral view, that area that lies between the lower end of the compound eye and the base of the mandible (Fig. 0, MA).
Mandible length - the straight-line length of the mandible, from base to farthest extent of outer margin (Figs. 0, 0, ML).
Media worker - Those individuals of the worker subcastes that are intermediate in size between Major and Minor workers.
Mesepisternum - the lateral surface of the mesothorax; often also called "mesopleura" or "mesopleuron".
Mesonotum - the dorsal surface of the mesothorax; in alate forms the mesonotum consists of the mesoscutum and mesoscutellum.
Mesosoma - the middle portion of the insect body; often erroneously called the "thorax" in older literature on aculeate Hymenoptera; now often called "alitrunk" or "truncus" in current ant literature. We prefer mesosoma in order to be consistent with growing usage in other groups of aculeate Hymenoptera; it is a morphologically neutral term. See Metasoma.
Metanotum - the dorsal surface of the metathorax; often not distinguishable in worker ants but may be represented by the metanotal groove (Fig. 00).
Metapleural gland - a gland characteristic of ants, situated posteroventrally on the mesosoma; it is a source for antibiotic substances, at least in some ants (Fig. 00).
Metasoma - the posteriormost portion of the insect body; in aculeate Hymenoptera consisting of the second and following true abdominal segments (the first is immovably fused to the true thorax as the Propodeum, q. v.). In ants, the first metasomal segment (= abdominal segment II) is always modified to form the Petiole, which may bear a dorsal node or scale. In some ants, metasomal segment 2 (= abdominal segment III) may also be distinctly modified and differentiated from the following segments and is then designated the Postpetiole. The undifferentiated segments posterior to the Petiole or Petiole + Postpetiole comprise the Gaster. See Gaster, Petiole, Postpetiole.
Minor worker - the smallest worker subcaste in ants (sometimes called minima or minims).
Monogynous - with only a single functional nest gyne or queen (see Polygynous).
Monomorphic - worker caste not divided into subcastes, hence uniform in overall appearance (see Polymorphic).
Occipital lobes - see Vertexal lobes.
Occiput - see Vertex.
Ocelli - the three simple eyes situated on the vertex of female and male ants; usually ocelli are not present in worker ants.
Ocular Index (OI) - the ratio of eye length to head length as expressed by the formula (EL/HL)(100).
Oculomandibular distance (OMD) - the length of the malar area as viewed in profile; commonly compared against EL.
Pectinate - comb-like or bearing a comb of fine, closely set teeth.
Pedicel - the "waist" in ants, sensu Hölldobler and Wilson (1990), consisting of the Petiole + Postpetiole. Although not often used in ant taxonomy, the term is also applied to the second segment of the antenna of aculeate Hymenoptera; the third and following segments comprise the Flagellum; Pedicel + Flagellum = Funiculus as applied in ant taxonomy.
Pedunculate - set on a stalk or with a stalk-like base.
Petiole - the first segment, if two are present, of the"waist" of ants; morphologically the true second abdominal segment. See Metasoma.
Pilosity - the longer, stouter hairs or setae standing above the fine Pubescence, q.v.
Polydomous - referring to a single colony that simultaneously occupies more than a single nest site, such as a colony that dispersed within a number of twigs or branches of a single tree or shrub.
Polygynous - referring to the usual presence of two or more functionally reproductive gynes or queens within a single nest.
Polymorphic - in ants, the existence of a sufficiently broad range of worker individuals that those at either end of the range, although very different in appearance, are connected by a continuous series of intermediate forms.
Postpetiole - in certain ants (especially subfamily Myrmicinae) the second segment of the "waist"; morphologically the true third abdominal segment. See Metasoma.
Pronotum - in ants, the visible dorsal portion of the prothorax.
Propodeum - morphologically, the true first abdominal segment, now immovably fused to the thorax; has been called "epinotum", especially in earlier ant literature.
Proximal - Nearest the body or toward the base of a segment or structure.
Pubescence - the short, very fine hairs forming a second layer underlying the longer, coarser hairs; commonly appressed to the body surface.
Punctate - surface sculpture consisting of fine pits or punctures.
Pygidium - A modified, often plate-like, structure or area on the last dorsal gastral segment.
Reticulate - surface sculpture consisting of a network of carinae or rugae.
Ruga - a coarse, usually somewhat irregular, wrinkle on the body surface.
Rugoreticulate - rugae forming a coarse network.
Rugose - body surface with a number of rugae, often more or less parallel.
Scape - the first, basalmost segment of the antenna (Fig. 0, SC).
Scrobe - a deep groove or depression into which an appendage may be folded.
Serrate - with saw-like teeth along the edge.
Shagreened - surface texture is rough in appearance, suggestive of a shark skin.
Soldier - the large worker subcaste specialized for colony defense.
Spongiform - having the appearance of a sponge, as in the structures that partially cover or surround the petiole and/or postpetiole in many dacetine ants.
Spur - a spine-like appendage at the distal end of the tibia; one or two may be present.
Squamate - scale-shaped, as in squamate hairs.
Sternal - refers to the ventral gastral segments.
Striae - fine impressed lines on the body surface; often so fine as to impart a silky or satiny appearance to the surface.
Striate - body surface with a series of parallel striae.
Suberect - refers to body hairs at an angle of about 45o from the body surface (Fig. 0).
Sulcus - a deep furrow or groove.
Tarsus - the foot of an insect; five-segmented in ants; the basal segment is the basitarsus.
Taxon - any taxonomic entity, such as a particular genus or species.
Tergal - refers to the dorsal segments of the gaster.
Tibia - the fourth leg segment, between the femur and the tarsus.
Trochanter - the second, very short, leg segment, between the coxa and the femur.
Tuberculate - body surface covered with tubercles (short, thick spines or erect pimple-like structures).
Venter - the lower (ventral) surface of the body.
Vertex - the top of the head, often incorrectly called the occiput.
Vertexal lobes - the prominent dorsolateral angles of the head, often called occipital lobes, separated in the middle by a distinct concavity when head is in frontal view (Fig. 00).

     HEAD (Figures 1-9)
Eye length (EL). The greatest length of the eye, usually taken in lateral view (Fig. 3)
Head length (HL). With head in frontal view, the maximum length along the midline, from the anterior clypeal margin to the vertexal margin. The head, in this position, is in full frontalview (Fig. 2).
Head width (HW). With head in full frontal view, the maximum width along a line perpendicular to that of HL, exclusive of the eyes (Figs. 2, 4).
Interocellar distance (IOD). The minimum distance between the inner margins of the posterior ocelli (Fig. 4).
Minimum ocular diameter (MOD). The minimum diameter of the compound eye, measured perpendicular to EL.
Ocellar diameter (OD). The maximum transverse diameter of the anterior (middle) ocellus.
Ocellocular distance (OOD). The minimum distance between a posterior ocellus and the nearest compound eye (Fig. 4).
Oculomandibular distance (OMD). The distance between the lower margin of the compound eye and the nearest point of the base of the mandible (Fig. 3).
Mandibular teeth. The lower or outermost tooth is the longest and sharpest as a rule; this is the apical tooth (apl). The upper, or innermost, tooth is the basal tooth (bsl). Of the remaining, middle teeth, that nearest the apical tooth is the preapical tooth (papl); that nearest the basal tooth is the subbasal tooth (sbsl) (Fig. 9).
Psammophore (psm, Figs. 6, 7). Located on the posterior surface the head and the posterior margin of the mandible. Two types:
1. Complete: a row of very long, flattened, curled, closely spaced setae is present along the posterior margin of the gena. These setae extend over the gular area and are
supplemented by similar setae along the margin of the mandible (Figs. 63-68). The enclosed gular area is flattened, devoid of hairs and smoother than adjacent areas of the gena.
2. Incomplete: gula is usually more or less convex, often not sculptured differently from adjacent gena and short hairs may be present; the long setae are widely spaced and often do not completely enclose the gular area nor do they always extend the full length of the underside of the head. In Dorymyrmex (Fig. 7) and Myrmecocystus (Fig. 6) the maxillary palpi are elongate, beset with long bristles, and are folded back along the gular surface to supplement the incomplete psammophore.
Scape length (SL). The maximum length of the antennal scape, exclusive of the basal condyle (bslc) (Fig. 5).
      Antennal segments are numbered 1-n, with the scape as the first segment. Segments beyond the scape are commonly called the funiculus but that term is not used here. The last 2, 3, or 4 segments may be enlarged to form an antennal club (Fig. 5). The following indices are used:

Cephalic index (CI): (HW) (100/HL).
Ocular index (OI): (EL) (100/HL).
Scape index (SI): (SL) (100/HW).
Figures 1-9. Abbreviations
antc - antennal club 1p - labial palp
ants - antennal socket mdls - mandalus
apl - apical tooth (mandible) mlcl - middle lobe of clypeus
atp - anterior tentorial pit mlra - malar area
bsl - basal tooth (mandible) mndl - mandible
bslc - basal condyle of scape mxp - maxillary palp
bsll - basal lobe of scape OOD - ocellocular distance
cly - clypeus papl - preapical tooth (mandible)
frc - frontal carina sbsl - subbasal tooth (mandible)
frl - frontal lobe sca - supraclypeal area
frmg - foramen magnum SL - scape length
glrt - gular teeth tllm - trulleum
HL - head length vtx - vertex
HW - head width vtm - vertexal margin
INOD - interocular distance
IOD - interocellar distance
llcl - lateral lobe of clypeus

     MESOSOMA (Figures 11-15)
     
      The mesosoma of the worker ant, although much modified, is usually more or less definitely divided into several segments. The prothorax is represented by the pronotum, distinct at least at the sides. The mesonotum is often distinctly separated from the pronotum by the promesonotal suture; when the two are fused, the resultant structure is the promesonotum. The side of themesothorax, the mesopleuron, is always free of the propleuron,but fused with the metapleuron, through the mesometapleuralsuture. Posteriorly, the metapleura is fused with the side of the propodeum, usually without a visible external suture. Dorsally, the metanotum, when visible, is a narrow transverse
band immediately posterior to the mesonotum. This is followed by the propodeum (= epinotum of earlier literature), which may be tuberculate or bispinose at the junction of the dorsal and posterior faces.
     The mesosoma of female and male ants is usually much more normal, with the usual, recognizable structures of aculeate Hymenoptera; refer to Figures 13-15.

     Figures 11-15. Abbreviations
ax - axilla ppm - propodeum
mes - mesoscutum (mesonotum) pps - parapsidal suture
met - metanotum ppt - postpetiole
mf - Mayrian furrow prn - pronotum
msp - mesopleuron prsp - propodeal spiracle
mtp - metapleuron pt - petiole
mtsp - metathoracic spiracle sppt - subpostpetiolar process
not - notaulus spt - subpetiolar process
paps - parapsis teg - tegula

     PETIOLE (Figures 11, 14, 16-19)
     One-segmented in Ponerinae, Dolichoderinae and Formicinae;
two-segmented in Ecitoninae, Pseudomyrmecinae, and Myrmicinae. The first segment is the petiole. When a second segment is present, it is the postpetiole. The dorsal portion of the segment(s) is elevated to form a node or scale, depending upon its shape. Ventrally, the segments may possess subpetiolar and/or subpostpetiolar processes, often tooth-like or spiniform when seen from the side.
     These segments are, morphologically, the true second and third abdominal segments. The true first is immovably fused to the mesosoma as the propodeum.

     GASTER (Figures 16-21).
     The remaining metasomal segments are the gaster. In females a sting is present except in the Dolichoderinae and Formicinae. The female castes of the latter have a structure at the apex of the gaster by which formic acid is sprayed in defense, the acidopore: dolichoderines possess an anal slit. Males, of course, have a genital capsule (Figs. 20, 21).

     Figures 16-21. Abbreviations
ac - acidopore pen- penis
aed - aedeagus pmr - paramere
as - anal slit ppt - postpetiole
cus - cuspis pt - petiole
dig - digitus sppt - subpostpetiolar process
br - basal ring spt - subpetiolar process
gs - gastric constriction bpmr - basiparamere
NOTE: cuspis + digitus = volsella (vol)

     THE KEYS

The keys are presented in the sincere hope that they will prove useful. Some are synthesized from preexisting keys, but most are newly prepared for this study. We are confident that most work well, provided care is taken to understand each statement. These keys are based on mounted, fully dry specimens and often the characters cannot be properly interpreted with specimens in fluid. All measurements are made with an ocular micrometer and anyone using the keys will find it necessary to utilize the same method.

     ILLUSTRATIONS
The figures which accompany this text are intended to supplement the keys and taxonomic discussions to illustrate features used in distinguishing between the various genera and species. Usually, simple line drawings are sufficient and details of sculpturing and vestiture are omitted. When such details are critical in identification they may be illustrated as supplemental figures (as in Fig. 38a).
     A few habitus figures were done by Ruth Ann DeNicola and we are grateful for the opportunity to use them. The remaining figures are the work of the senior author.

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