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Pterocanium prismatium Riedel, 1957

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Cephalis subspherical, pitted, bearing a sharply pointed, cylindro-conical apical horn with a length of approximately 1.5 times cephalic diameter, and sometimes smaller accessory spines. Thorax having overall shape of a triangular prism surmounted by an obtuse triangular pyramid, terminating at pronounced collar stricture: this general shape often modified by shallow concavity of the prismatic faces, and slight swellings between the proximal parts of the three thoracic ribs. In relation to the general thorax surface, the thoracic ribs are usually depressed in furrows proximally, and raised on ridges distally. Thoracic pores subpolygonal to almost circular, separated by thin bars, arranged approximately hexagonally in apparent longitudinal rows. Upper part of thorax usually bears small spines: these spines often concentrated on the proximal swellings, and thorns often occur on the ridged part of the thoracic ribs. Opening at base of thorax somewhat constricted. Feet three-bladed, proximally fenestrated, straight or slightly curved, usually almost parallel or somewhat divergent, usually shorter than thorax. Abdomen, when present, short, delicate, with irregular meshes smaller than those of thorax, usually entirely separate from and surrounded by the feet.
Usual length of apical spine 28-40, of cephalis 20-26, of thorax 110-132, of fett 60-120, of abdomen 5-50. Breadth of thorax usually 110-150.
This species is readily distinguished from most others of the genus by the generally prismatic form of the thorax. It differs from Pterocanium virgineum Haeckel and O. praetextum (Ehrenberg) in the relatively shorter feet and larger thorax.
Riedel 1957











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