Ch. macrophthalmus Schm. pl. VII, figs. 1 c, 2. Faint indications of narrow pits.
Ch. Quenstedti Barr. Tab. 42 fig. 3. Maculæ near lower border as two narrow slits.
Ch. spinulosus Schm. pl. VII fig. 10. The lateral pits well visible.
Ch. tumidus Schm. pl. VIII, fig. 22. The pits are short, but present.
The exterior surface of the hypostoma is entirely covered with small wartlets, closely set, of different size in the various species, and spread between them lie a great number of elongate smooth spots dispersed, on the interior side of the hypostoma showing an excavated surface ([pl. III fig. 16]).
Chirurus (Cyrtometopus) clavifrons Dalm.
The shape of the hypostoma is shown in [fig. 21 pl. III]. It is regularly shield-formed with posterior margin rounded. A shallow groove running parallel with the margins forms a large, faintly elevated border. The anterior margin projects on both sides in a short, backwards directed, broad and fiat wing, hollowed out with a pit on the front side, and there is a posterior lateral wing, midways between the anterior and posterior margin short, blunt, directed obliquely backwards. The whole exterior surface is covered with diminutive tubercles, the above mentioned smooth spots interspersed on the central disk. A little below the middle there are two lengthened pits, so shallow that they often are not discernible. In a specimen of Chirurus spinulosus Nieczkowski from Estland there are two, almost 3 mm. long dots, one on each side above the maculæ as the [fig. 21] shows and in several others of this generic group there are also indications of similar. I cannot compare these dots with anything more than the lengthened spots visible in Acidaspis crenata.
The maculæ are wanting in this species, but the cephalic eyes are well developed. A section of them [fig. 19] shows the enormous difference of the shell in the eye and the surroundings where the shell surpasses it many times in thickness. The eye consists in fact only of the ovate, beadlike lenses of which a string is seen sectioned in the figure mentioned. More enlarged ([fig. 20]) a nucleus is visible in each lens, and in a horizontal section ([fig. 18]) a little below the surface, where they are more pressed against themselves, they have a polygonal shape. The [figure 17] seems to represent lenses that have been much changed interiorly, having only a narrow zone left of the primary structure.
Chirurus glaber Angelin.