530 bulletin: museum of comparative zoology. 



are short, while the third pair are stronger, and turn abruptly back to 

 join the neck-furrow, thus isolating a pair of small, nearly square lobes 

 at the base of the glabella. The other furrows are deep at their junc- 

 tion with the dorsal furrows, and thus form small, node-like side 

 lobes. There is some variation in the course of the posterior pair of 

 furrows. In the majority of specimens they turn back to the neck- 

 furrow, but in a few they become very faint at the inner ends, so that 

 the posterior lobes do not appear to be isolated. The fixed cheeks are 

 convex, highest at the eye, and bear the genal spines. The free 

 cheeks are small, the sutures reaching the anterior margin at points 

 but little behind the eyes. A facial suture leaves the anterior margin 

 where each dorsal furrow intersects it and runs outward and backward 

 on the arc of a flat ellipse, encircles the top of the eye, then runs almost 

 straight to the margin again, reaching it a little behind the horizon 

 of the eyes. The eyes are small, minutely faceted, high, and promi- 

 nent, and have eye-lines which originate opposite the first pair of 

 glabellar furrows and extend to the palpebral lobe. The eyes are 

 situated far forward on the cheeks, and a little nearer to the glabella 

 than to the posterior margin of the cephalon. The distance of the 

 back of the eye from the posterior margin was found, by measurement 

 of many specimens, to be from .40 to .58 of the length of the glabella. 

 The curvature of the head makes the cheeks shorter than the glabella, 

 so that the eyes are really very close to the anterior margin. The 

 neck-furrow is narrow and deep on the fixed cheeks, and on the sides 

 of the glabella, but faint on top. The whole cephalon is surrounded 

 by a convex border which is rather wide on the cheeks, but very narrow 

 in front of the glabella. 



The surface of the cephalon, barring the genal spines, is covered 

 with pits and tubercles of various sizes. On the glabella, there are, 

 beside the numerous irregularly placed ones, two rows of coarse 

 tubercles which are in a rough alignment. These rows diverge toward 

 the front. The fixed cheeks have many tubercles and pits, and 

 behind, and a little inside the eyes, are two small but prominent 

 tubercles on a line parallel to the axis of the animal, and a little inside 

 the line of nodes marking the fulcra of the thorax. On many speci- 

 mens there is a tubercle on the posterior border in line with these. 

 Well preserved specimens show three or four spine-like tubercles on 

 the posterior border of the cephalon. The surface of the genal spines 

 is granulose. 



The thorax is composed of eleven segments, the axial lobe convex, 

 and marked by two rows of small nodes. The pleural lobes are 

 divided into two parts, an inner, solid and nodose portion, and an 



