Genus Siagoninm Kirby
Siagonium Kirby, in Kirby and Spence. Introduct. Ent., 1, 1815. Prognatha Latr., in Cuvier, Regn. Anim., 4, 1829, 439. Body moderately long, depressed or lightly convex. Head moderate,
transverse, with rather small and somewhat prominent eyes, slightly narrowed behind. In males normally with each anterior angle produced into a stout, forwardly (and sometimes inwardly*) directed horn; in some species, at least, small male forms occur which have the anterior angles rounded and simple; there are also intermediates between these and the normal form. Head of female as in small male forms. Gular sutures converging at base and diverging in front, becoming very approximate in middle. Antennae long or very long, not thickened apically, longer in large males than in small males, slightly longer in small males than in females; the first segment distinctly stouter than the following. Labrum short, transverse, the front margin broadly emarginate; chitinized except towards anterior angles; the chitinized portion bearing a few setae, the membranous portion fringed internally with close-set, short, fine hairs. Mandibles stout and pointed apically, the left with a small tooth internally about middle, the right unarmed internally. In the males, each mandible bears externally near apex a long curved, forwardly and slightly upwardly directed horn which in large specimens is longer than the mandible itself; mandibles of females unarmed externally. Inner lobe of maxilla (lacinia) narrow, with a few lightly curved spinules and a bunch of ciliae at apex internally, the outer (galea) rather narrow, densely ciliate apically, the ciliae being lightly curved at the tips and arranged in rows (Fig. 8).
Maxillary palpi with the first segment very small, transverse, the second about twice as long as first, about as long as broad, widened apically, the third about three-quarters as long as second, slightly widened apically, the fourth more than twice as long as third, bluntly pointed. Mentum transverse trapezoidal. Glossae and paraglossae fused, forming two divergent lobes which are ciliate internally, the ciliae being distinctly curved. Between these lobes is a longitudinal, chitinized strip and on each side of this a small subquadrate chitinized sclerite and. anteriorly, a strong seta (Fig. 11). Lobes of the hypo-pharynx well developed, densely ciliate internally and extending to transverse, the apex of the ligula. Labial palpi short, the first segment short, transverse, the second shorter and slightly narrower than first, the third about two and a-half times as long as and slightly narrower than second, bluntly pointed. Pronotum transverse, sinuate before the well-marked posterior angles, the epipleura narrow. Epimera triangular, fused with the epipleura and projecting inwards to about the middle of each coxal cavity. Prosternum rather large, the pro-sternal suture well marked, basisternum not keeled, furcasternum deflexed inwards (towards the dorsal) from the plane of the basisternum and furnished with a well-marked longitudinal median keel which projects between the anterior coxae. Mesosternum short, with an indistinct median longitudinal keel. process narrow and pointed, slightly overlapping the metasternal process in some species, e.g. S. quadricorne Kby. (Fig. 4) or extending only as far as the middle of the coxal cavity in others, e.g. S. vittatum Fol. (fig. 15). Meta-
[Footnote] * In some species, e.g. S. vittatum Fvl. (Fig. 3) and S. americanum Melsh. (Fig. 2), the horns appear to originate from the front of the head between the anterior angles, but, on closer examination, can easily be traced to these angles.
sternum long, with a short, pointed, anterior process which projects between the intermediate coxae. Scutellum well marked. Wings well developed. Elytra rather long, parallel sided, with well-marked epipleural folds. Tergite of second abdominal segment short, lightly chitinized. Third to sixth (first to third visible) segments about equal in width, the abdomen narrowed thence to apex. Seventh segment distinctly longer than the sixth. Paratergites present on segments three to seven. Sternite of third segment with a well-marked median longitudinal keel. Legs rather short, the coxae rather small, the anterior globose, somewhat exserted, with a semi-circular sulcus before apex, the intermediate oval, the posterior expanded laterally above (dorsal to) and with a small lateral expansion below (ventral to) the level of the femora; all the coxae contiguous. Femora moderate, the anterior slightly widened at apex internally above and below the level of the tibiae. Anterior and intermediate tibiae with a few spines externally, the anterior with a well-marked eurved spur at the anterointernal angle, the posterior with a few setae externally and three or
four spines at apex. Tarsi five-segmented, about half the length of the tibae, the first four segments short and subequal in length, the fifth longer than the four preceding together.
Genotype: Siagonium quadricorne Kby. (monobasic). (Fig. 1.)
Range: Europe, Japan, North America, ? India.
The two European species, S. quadricorne Kby. and S. humerale Germ., show a marked degree of polymorphism in the development of the head in the male. It seems likely that this would also be true for
the other species, but, as it has yet only been possible to examine very small series of these, one cannot be absolutely certain. The large males with well-developed cephalic horns occur in all species.
The species occur under the bark of various trees.