A superbly preserved group, possibly a mating assemblage, of Phacops rana from the Silica Shale of Sylvania, Ohio (x0.77). (Photographed by the author, through courtesy of David C. Rilling.)

Phacops rana rana Green (x2.3). Moscow Shale, Devonian, Springbrook, Erie County, New York (loaned by FMNH). Print obtained from color slide. In conttast to the ptevious assemblage of intact individuals, clearly a sudden mass burial of living trilobites, this assemblage contains partially disarticulated carapaces. These could be either exuviae or the result of post-burial tewotking of the sediment, possibly by scavenging otgamsms.

Many trilobites from Morocco appear as magnified versions of congeneric, contemporaneous individuals from other localities. This is the case with the giant Devonian Phacops (Drotops) megalomanicus (Struve), from AJnif, that has pervaded the trilobite market in astounding abundance. At least two, possibly more species may be represented. The example shown in side view in this plate (x 1.4) shares most of its characters with the examples of Phacops shown in the preceding plates, except for its size. The tuberculation of the convex parts of the carapace is particularly prominent. The pairing of several pleurae and consequent rotation of the corresponding axial rings gives the impression of strain, possibly of interrupted locomotion, suggesting that articulation of the segments may have been functional in more ways than just for enrollment. Specimen whitened with magnesium oxide. (RLS coll., prepared by the author.)

Another well-prepared example of the giant Phacops (Drotops) megalomanicus (Struve) from Alnif, Morocco (xl.5). The thick carapace is usually preserved as dark calcite, sometimes coated by a whitish patina. This specimen is lightly varnished. (Photographed by the author, through courtesy of David C. Rilling.)

The second of the clearly distinct Devonian, Phacops-Yike species, possibly a new genus, from Alnif, Morocco, is shown in this photograph (x 2.6). The distinctive character here is the alignment of very prominent tubercula into rows, extending longitudinally along the pleural field and axis, continuing into the pygidium. There are two symmetrically arranged rows along the axis, two along each pleural field. The pleural margins are otherwise smooth. This enrolled specimen has been whitened with magnesium oxide. (RLS coll.)

Family Homalonotidae c" £ ^'l aPman', , 8 9 0

Subfamily Homalonotinae E. J. Chapman, '189(0

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