There is not the least evidence to support the suggestion that the »ocular ridge» is homologous, with the eye of Apus[16] and that the real crystal cones lay sunk beneath the surface in a »water sac». As we, for instance, in Peltura have an »ocular ridge» (= facial ridge _mihi_) on the fixed cheek and opposite its posterior extremity, the »eye lobe», a real eye with facets on the free cheek it is not likely to suppose that the »ocular ridge» nor the »eye lobe» ever functioned as a visual organ or that two widely different sorts of eyes were placed in closest vicinity opposite each other. [Footnote 16: BERNARD, The systematic position of the Trilobites. Qu. Journ. Geol. Soc. 1894, p. 411.] It may be worth while here to remind of the great similarities, whether analogous or homologous, in the formation of the superior surface of the head in the trilobites and the embryons and the newly hatched larva of Limulus. The latter have the head shield separated into five portions, partly through a facial suture which, as in Peltura, Dalmanites and others, forms a continuous line around the glabella. This suture divides the eye node in a similar way as in the trilobites, that is, sectioning it in two parts, of which one adheres to the central fixed cheeks and the other to the free cheeks.[17] And to judge by the figures of KINGSLEY the former, the whitish moiety is the first developed and sometimes for a while quite alone as the facial ridge of the trilobites and probably also anterior to the suture, as this is not complete at this stage. This white node reminds of the small facial ridge in Arionellus ceticephalus BARR. [Footnote 17: PACKARD, Development of Limulus polyphemus. Memoirs Boston Soc. Nat. H. vol. II, pl. V, fig. 25. Nothing is said about the exterior structure of the eyes. DOHRN, Zur Embryologie and Morphologie des Limulus Polyphemus. Jenaische Zeitschrift 1871. A very good figure (pl. XIV, f. 4) shows clearly the two parts of the eyes, the interior one being larger. KINGSLEY also (Devel. of Limulus, Journal of Morphology, vol. 7, 1892, pl. VI, fig. 34) has in the last larval stage the suture and the eye in two parts, of which one is white lying inside the suture and the eye proper, black, outside.] As KISHINOUYA[18] has already pointed out and as I have anticipated above the head of the most developed trilobites in their adult state, and the head of the larval Limulus consists of five parts, viz. 1) the glabella in the centre, 2 & 3) the fixed cheeks, 4 & 5) the free cheeks. An elevated ridge in the adult Limulus shows where the suture once lay and it is on the outside thereof that the eye of the adult is placed. What other authors call the ridge or the eye ridge in Limulus, KISHINOUYA rightly names a suture. [Footnote 18: Journal College of Science Tokio, vol. V, p. 53, 1892.]