CHEIRURUS. 65 



moderate size, half as long as the entire glabella, and on the sides overhanging the other 

 lobes ; in front it is somewhat produced, and occupies all the margin. The glabella is 

 neither gibbous nor depressed, a line taken from the front edge to the neck-furrow pre- 

 senting a regular and gentle convexity. Cheeks subtriangular, not so wide as long, with 

 a broadish margin distinctly separated by a furrow, which meets the strong, straight neck- 

 furrow at the posterior angles ; these angles are spinous, the spine short and directed 

 backwards. The eye is placed more than half way up the cheek, and not close to the 

 glabella ; it is opposite the middle furrow, and is rather small, supported by a raised rim 

 below ; the eyelid is narrow and indented, the lentiferous surface very convex, supine, and 

 covered with minute, closely set, convex facets, with no spaces between them. In 

 some specimens each facet has a minute pit upon it, but this is due to wear; the lenses 

 being regularly convex when perfect. These are figured in the Survey Decades. Above 

 the eye the facial suture takes a vertical course, and cuts the margin exactly where the axal 

 furrow ends on it ; below the eye it turns directly outwards to the smooth border, which 

 it cuts considerably in advance of the posterior angle, and in an oblique direction, so that 

 it reaches further back on the lower side than on the upper. 



We do not know the course of the suture in front; it is probably direct across, 

 beneath the front margin, and Barrande describes a rostral shield on the under surface. 

 The surface of the glabella is sparsely covered with small granules (fig. 9), the cheeks are 

 largely scrobiculate, and the wings or free cheeks have their border smooth, and only 

 scabrous on its outer edge ; they are sometimes dilated a little in advance of the facial suture. 

 Labrum (PI. VI, figs. 12, 13) large, ovate, oblong, very convex; its length generally one 

 fourth more than the width, but in appearance often more ; broadest near the strongly arched 

 base of insertion, from which the central convexity rises immediately, and reaches nearly to 

 the tip. A rather deep furrow surrounds the central portion, and separates it clearly from 

 the more or less tumid margin. The furrow becomes deepest near the rounded shoulder, 

 which we have called the ' auricle,' followed by a deep notch, above which the ascending 

 processes {a, a) take their origin. The apex of the labrum is truncate, the corners angular, 

 or even mucronate. Besides the distinct sulcus, which separates the border all round, 

 there is a short oblique furrow higher up on each side. The whole surface of the labrum is 

 closely scabrous (PI. V, fig. 5) ; the convex portion has, besides, scattered, larger granules. 

 The organ is hollow when viewed from the inner side (PI. VI, fig. 13), and the structure there 

 observable is such as has been described by Barrande. 1 There are two ascending pro- 



1 M. Barrande, 'Neues Jahrbuch.,' 1847, p. 389, has given a full description of the 'hypostome' 

 of Cheirurus. He describes the ascending processes a, a (Fiiigel), as bent upwards at right angles to the 

 surface of the organ, and uniting with the upper crust along the line of the dorsal or axal furrow, with 

 a broad base of attachment, reaching from the upper to the middle glabella-furrow. In Phacops it has 

 nearly the same position. He also describes a second organ, of the same size and shape, but less convex 

 in all its parts, lying immediately behind the hypostome, between it and the upper crust of the head. 

 This organ he calls " epistoma ;" and he has seen it both in Cheir. insignis and a species of Phacops. It has 



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