Walcott, 1888. Zacanthoides typicalis Walcott (xll). Chisholm Shale, M. Cambrian, Half Moon Mine, Pioche, Nevada. (Specimen collected by Afton Fawcett. RLS coll., id., now at FMNH.) Once again it is worth showing the comparison berween standard photography of the specimen in air (a) and what can be seen with xylene immersion (b). The long axial spine originates from the eigth thoracic axial ring.

Zacanthoides typicalis

Walcott (xl5.8). Same origin as for preceding plate. (Specimen collected by Afton Fawcett. RLS coll., id., now at FMNH.) The trilobite exoskeleton is partly preserved on both sides of the bedding plane. With the aid of xylene immersion, the parts which are missing in (b) can be identified in (a), so that a complete reconstruction can be obtained.

Family Dorypygidae Kobayashi, 1935 plate 75

OLENOIDES Meek, 1877. Olenoides servants Rominger (xl.8). Burgess Shale, Stephen Formation, M. Cambrian, British Columbia. (Loaned by MCZ.) Photography of the same pair of trilobites by two approaches: (a) by standard technique; and (b) while immersed in xylene. Note the power o the second method in revealing details the contour of the carapace. The trilobites from this famous locality are often found with soft parts preserved.

Unfortunately, this specimen does not show the appendages often seen emerging from the edge of the carapace. Compression of the glabella outlines the underlying hypostoma.

A striking example of Olenoides superbus Wal c o 11 from the Marjum Formation, M. Cambrian, east side of Wheeler Amphitheatre, House Range, Utah (xl.8). (Photographed by the author, through courtesy of Eddie Cole, who collected and prepared the specimen.)

Family Dolichometopidae Walcott, 1916

BATHYURISCUS Meek, 1873. Association of Batbyuriscus fimbriates Robison (right and left) with Modocia laevinucha Robison (center) (x2.7). Marjum Formation, M. Cambrian, between Marjum pass and Antelope Springs, Millard County, Utah. (Collected by Afton Fawcett. RLS coll id., now at FMNH.)

yuriscus Robison (x6.3). Same origin as previous plate. (Collected by Afton Fawcett. RLS coll., id., now at FMNH). One of the missing libriginae overlaps, over-turned, the right-hand side of the thorax, showing prominent radiating alimentary diverticula (prosopon).

A complete exoskeleton of Bathyuricus Robison (xl2). Same origin as previous plate (collected by Afton Fawcett, RLS coll., id., now at FMNH).

HEMIRHODON Raymond, 1937.

Hemirhodon amplipyge

Robison (x2.1). Marjum Formation, Marjum Pass, Millard County, Utah. (Collected by Alton Fawcett. RLS coll., id., now at FMNH.) A beautiful example of this large trilobite.

Family Ogygopsidae Rasetti, 1951

plate 81

OGYGOPSIS Walcott, 1889.

Ogygopsis klotzi (Rominger), M. Cambrian, British Columbia (x2.0). (Latex mold of specimen loaned from MCZ.)

Family Paradoxididae Hawle and Corda, 1847

Subfamily Paradoxidinae Hawle and Corda 1847

plate 82

PARADOXIDES Brongniart, 1822. Paradoxides paradoxissimus (Wahlenberg), M. Cambrian, Oltorp, Vastergotland, Sweden (xl.4). This is the type specimen, preserved in black alum shale, described in Westergard (1952), pi. 8, fig. 2, originally Paradoxides tessini Brongniart (SMNH No. Ar 47487). The upper specimen is an external impression

(photographed by the author at SMNH, through courtesy of Jan Bergstrom).

Colorful preservation of the exuviae in another example of Paradoxides paradoxissimus (Wahlenberg), from the same locality as plate 82 (x0.84). (Photographed by the author at the Paleontological Institute, University of Uppsala, Sweden.)

Developmental stages (late meraspid degrees) in the Middle Cambrian trilobite Paradoxides gracilis (Boeck), M. Cambrian, from Jince (Jinetz), Bohemia. The specimen in (a) (x8.6) exhibits much elongated genal spines as well as pleural spines of the second thoracic segment. The latter character is common to meraspid stages of other paradoxidids (see plate 92) and is reminiscent of the long pleural spines associated with the third segment macropleurae observed

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