phacops btssett. 157 



4. Phacops (Chasmops) bisseti, sp. nov. Plate XX, figs. 1 — 3. 



Specific 0/iaracfers.— Head-shield transversely semicircular, more than twice as 

 broad as long, gently convex. Glabella scarcely raised above cheeks, triangular in 

 shape, twice as wide at front end as at base; length considerably less than width 

 at front end. Frontal lobe large, rather flattened in front, transverse, short, more 

 than two and a half times as wide as long; lateral angles overhanging "cat's ear"' 

 lobes, and projecting laterally to facial sutures, and nearly overhanging the eyes; 

 V-shaped mark, composed of coarse puncta, on frontal lobe. The "cat's ear " lobes 

 extend rather more than half along the sides of the glabella, and their inner angle, 

 where they unite with the central portion of the glabella, is about 70° and is 

 mnrked by a rather prominent tubercle, while the posterior lateral angle made with 

 the axial furrow is nearly 90°. First lateral furrows slightly undulating, and 

 making between them angle of 120° — 130° ; not meeting the shorter second lateral 

 furrows. Central portion of glabella between inner angles of " cat's ear " lobes 

 less than one third total width of glabella. " Second" x lateral lobes represented 

 by small prominent nodules near inner ends of second lateral furrows. "Third" 

 lateral lobes represented by faint swellings on a transverse rounded band behind 

 the " cat's ear " lobes. Neck-ring rounded, marked off by strong occipital 

 furrow from this transverse band, and about half as wide again as the latter. 

 Axial furrows strong, diverging anteriorly from neck-ring at about 75° — 80° 

 as far as the first lateral furrows, in front of which they bend outwards 

 round the overhanging angles of the frontal lobe. Surface of glabella finely 

 granulated with numerous large coarse tubercles, scattered freely over it. 

 Cheeks triangular, nearly as high as glabella, with the usual characters found in 

 Chasmops. Lateral margins of head-shield strongly bent down; and free cheeks 

 furnished with long, broad, flattened, genal spines, closely pressed against body, 

 and extending back to at least the eighth thoracic segment. Surface of cheeks 

 granulated and rather coarsely pitted. Eye of moderate size, strongly curved, 

 high, conical, with its base at the level of the second lateral furrow, and its front 

 end about two thirds of the way up the "cat's ear" lobes. Eye-lobe very 

 prominent, and bent up along anterior and posterior edges. Visual surface of 

 eye composed of about thirty vertical rows of lenses, with twelve to fourteen lenses 

 in the highest rows. 



Thorax of eleven segments, half as long again as head-shield. Axis rather 



1 The author would prefer to call the lateral portions of the frontal lobe the first pair of lateral 

 lobes and the "cat's ear" lobes the second pair, making the so-called "second" lateral lobes really 

 the third. But to avoid confusion the commonly accepted terminology is here employed, though he 

 believes the homology implied is erroneous (see 'Quart. Journ. Geol. !>><'.,' vol. lviii, 1902, p. 64). 



