148 G. F. MATTHEW : ILLUSTRATIONS OF 



the eyelobe is outward toward the marginal fold, but it curves forward before reaching that 

 point ; behind the eye, the suture makes an open sigmoid curve, cutting the margin at a 

 distance from the outer margin of the cheek about equal to three quarters of the cord of 

 the eyelobe ; the distance between the extremities of this part of the suture is nearly equal 

 to the entire breadth of the cheek ; the length of the spine which is turned outward, is 

 equal to the anterior transverse diameter of the cheek. 



Sculpture. — The surface is punctate, but often exhibits faint, scattered tubercles like 

 those of the middle piece of the head-shield. There is a transverse wrinkling of the 

 margin of the cheeks on the inner slope of the marginal fold, which often simulates a 

 series of tubercles, but appears to be connected with the radiating raised lines that diverge 

 from the eyelobe, and form a faintly marked net-work over the surface of the cheek after 

 the manner of Anomocare micropthalmum of Angelin. In the movable cheeks of young indi- 

 viduals, it is almost impossible to distinguish this form from the broad form of the species, 

 owing to the narrowness of the cheeks in young tests of both forms. 



Thorax. — An example with the cephalic shield and five adjoining segments of the 

 thorax has been obtained, these exhibit the following characters. The first three pleurae 

 are short-pointed, but the succeeding segments are bluntly rounded as in Solenopleura, 

 and are broadened on the inner side near the tip by a sliding facet. As Liuuarssou has 

 remarked, they are narrow and but slightly bent downward, and a little bent backward ; 

 they carry rows of small spines along the edges, such as he found in the Swedish 

 examples. The furrow on the pleura, broad and open at the inner end, gradually deepens 

 and becomes sharper toward its outer end, which is close to the tip of the pleura. The 

 pleura is about twice as long as the ring of the rachis, which is traversed by a deep, 

 strong channel, the posterior bordering edge being ornamented with a row of minute 

 tubercles. 



Pygidium (Plate II, fisr. 2c). — This part of the body possesses a strongly marked rachis 

 crossed by five furrows, dividing olF five rings beside the half ring at the anterior end ; 

 the first two rings are strongly defined, but the three posterior are separated only by faint 

 furrows ; the last ring or lobe descends to an obtuse point at the end of the pygidium. 

 In some examples, the slope of this lobe may be seen to have three slight tubercles, two 

 in front (lateral) and one behind (axial) indicating that this lobe contains the rudiments 

 of two rings, making, with the preceeding rings of the axis, the lull number of rings 

 observed by Linnarsson in an example from the Microdiscus Scanicus slate in Sweden. 



In the ordinary type of the pygidium in the narrow form, the two anterior rings are 

 widened and somewhat inflated at the ends, giving the ends of the rings the appearance of 

 tubercles. The pairs of sulcate costœ in the lateral lobes described by Linnarsson, but not 

 mentioned by Brogger, are plainly shewn in the Acadian examples ; at the back of these 

 two distinct costœ is a third, short, broad and backward-bent rib, crossed diagonally by a 

 faint furrow. All these ribs, as well as the projecting parts of the axial rings, have rows of 

 minute spines or tubercles. The furrows of the lateral lobes are more sharply impressed 

 on these pygidia than on those of the broad or typical form. 



Length of the middle piece of the headshield, 12 mm. "Width, 16 mm. Movable cheek, 

 2| X 9 mm. Pygidium, 3J X 6 mm. 



On some layers of the shale, the head-shields of the narrow form are far more abundant 

 than those of the broad, but the latter appears to be more generally distributed. 



