[182]. Figures showing this suture are given by Oehlert, Bull. Soc. géol. de France (3), xxiii., 1895, pl. 1, figs. 9, 12, 15.
[183]. Ann. Mag. Nat. Hist. (2) iv., 1849, p. 396.
[184]. Lindström, “Visual Organs of Trilobites,” Svenska Vet. Akad. Handl. xxxiv., 1903. Exner, Physiol. d. facett. Augen v. Krebsen u. Insecten, 1891, p. 34, pl. ii. figs. 18, 19.
[185]. Journ. Morphol. ii., 1889, p. 253, pl. 21.
[186]. Watase, Johns Hopkins Univ. Studies, Biol. Lab. iv., 1890, p. 290. Lindström, op. cit. p. 27.
[187]. A suture is said to be present at the external margin of the flattened cephalic border.
[188]. Goldfuss, “Beitr. zur Petrefaktenkunde,” 1839, p. 359, pl. 33, fig. 2d.
[189]. Spencer, Geol. Mag. 1903, p. 489.
[190]. For an example of this see Salter, Mon. Brit. Trilobites, 1864–83, pls. 15, 16.
[191]. Bull. Mus. Comp. Zool. Harvard, viii., 1881, p. 191.