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Published online by Cambridge University Press: 01 May 2009
The genus Cheirurus offers an interesting study in evolution. Barrande, in his monumental work on the Silurian System of Bohemia, drew up a classification of the genus based principally on the character of the pleural grooves. Thus he divided the species into two sections—
page 117 note 1 Syst. Silur. Bohême, vol. i: Trilobites (1852), p. 770; and Suppl. to vol. i (1872).Google Scholar
page 117 note 2 Revis. d. Ostbalt. Silur. Trilob. 1881, pt. i, p. 121.
page 118 note 1 In Pseudosphærexochus these puncta are very faint or absent.
page 119 note 1 The type specimens on which the species was founded are not sufficiently well preserved for one to be sure of the number of segments—a point Salter notices.
page 119 note 2 The pygidium with seven segments ascribed to this species (Salter, Mon. Brit. Trilob. Pal. Soc., pl. v, fig. 21, p. 75) probably belongs to a distinct species, or even subgenus; but our ignorance of the other parts of the other parts of the trilobite to which it belonged prevents us coming to a decision about its exact position.
page 120 note 1 It is remarkable that this group, which includes the earliest members of the genus occurring in the Bohemian basin, has not yet been found in northern Europe (see sequel).
page 122 note 1 Eichwald. Lethæa rossica, 1860, p. 1408, T. lii, fig. 31.
page 122 note 2 Hoffmann. Sämmtl. Trilob. Russl. in Verh. d. mineralog. Gesellsch. 1858, p. 30, T. i, fig. 5.
page 122 note 3 Nieszkowski. Zusätze z. monogr. d. Trilob. d. Ostseeprov. im Archiv. für Naturk., Liv. Ert und Kurt, 1858, Ser. I, Bd. ii, p. 376, T. ii, figs. 7 and 8.
page 122 note 4 Steinhardt. Die in preuss. Geschr. gef. Trilob. in Beitr. z. Naturk. Preussens. D. phys. ökonom. Gesellsch. z. Konigsb. 1874, p. 60, T. iv, fig. 17.
page 122 note 5 Quart. Journ. Geol. Soc., vol. xiii (1857), p. 209, pl. vi, figs. 13 and 14.Google Scholar
page 123 note 1 A case of extreme specialization in this group is Ch. subulatus (Linnarsson), in which the pygidium has only two pairs of free pleuræ.
page 123 note 2 Marr, , Nicholson, . The Stockdale Shales: Quart. Journ. Geol. Soc. 1888, vol. xl, p. 722, pl. xvi, figs. 7 and 8.Google Scholar
page 123 note 3 Salter. Mon. Brit. Trilob.: Pal. Soc. 1864, p. 72, pl. v, fig. 16.
