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Paradoxides
''Paradoxides'' is a genus of large to very large trilobites found throughout the world during the Mid Cambrian period. One record-breaking specimen of ''Paradoxides davidis'' is . It has a semicircular head, free cheeks each ending with a long, narrow, recurved spine, and sickle-shaped eyes, providing almost 360° view, but only in the horizontal plane. Its elongated trunk was composed of 19-21 segments and was adorned with longish, recurved lateral spines. Its pygidium (caudal shield) was comparatively small. ''Paradoxides'' is a characteristic Middle Cambrian trilobite of the 'Atlantic' (Avalonian) fauna. Avalonian rocks were deposited near a small continent called Avalonia in the Paleozoic Iapetus Ocean. Avalonian beds are now in a narrow strip along the East Coast of North America, and in Europe.〔
== Description ==
The exoskeleton of ''Paradoxides'' is large to very large, relatively flat, oval to inverted egg-shaped, and about 1⅓× longer than wide, with the greatest width across the genal spines. The headshield (or cephalon) is close to semicircular with long spines developing from the corners of the cephalon. As usual in trilobites, the dorsal suture runs along the top of the eye. As in all Redlichiina this suture runs from the back of the eye slightly outward to the rear margin of the cephalon (a state called opisthoparian) opposite the base of the pleural spines. From the front of the eye the suture describes a slight S-curve forward cutting the front margin in front of the eye. The central raised area of the cephalon (or glabella) is divided in the occipital ring furthest to the back, followed by the first lobe that is like the occipital ring defined by a furrow across the midline and two more lobes that have furrows that do not connect across the midline. The frontal lobe is the widest and shaped like a segment of a circular band. It almost reaches the frontal edge of the cephalon. The eyelobe is short, opposite the first to third glabelar lobes. ''Paradoxides'' has a palate (or hypostome) with its front aligned with the front of the glabella and connected to the doublure (a condition science calls conterminant). Exceptionally, the hypostome is even fused with the frontal part of the doublure (called rostral plate), a character that distinguishes it from all other trilobites, except some Cambrian Corynexochida such as ''Oryctocephalus'', and ''Fieldaspis''.
The articulate midpart of the exoskeleton (or thorax) consists of 19-21 segments. The axis is about as wide as each of the ribs (or pleurae) to its sides, not counting the spines at their tips, which gradually arch further back while slightly increasing in length, while the spines on the rear thorax segment are much longer, about twice as long as the associated pleurae, are directly entirely backwards, and extend convincingly beyond the pygidium.
The tailshield (or pygidium) is small and shows the axis with one or two rings and may be partially or completely fused to the last thoracic segment. The axis does not reach the rear margin of the pygidium and defines a U-shaped pleural field.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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