= TRILOBITES. ° 745 
Arges wesenbergensis.] 
The outer cheeks are abruptly convex below the eye, are there broadly grooved by a 
furrow which widens toward the margin, where it produces a rather deep emargina- 
tion of the periphery. Genal extremities recurved, tapering to an acute angle, 
but not narrowed on the posterior surface. Occipital furrow broad and distinctly 
defined. 
Figs. 62, 63.—Cranidium of Arges wesenbergensis. var. paulianus. x 3. 
The cephalon is covered with tubercles which are coarsest over the glabellar 
lobes; on the cheeks they become scattered, vary more in size, and the coarser are 
gathered along the posterior margin. No single specimen of the head retaining 
all these parts in apposition has been observed, but in the cranidia the size is 
about the same, an average glabella measuring 54 mm. in length; 64 mm. between 
the eyes. 
Of the thorax only a few scattered segments have been seen. 
Fig. 64.—Pygidium of a somewhat smaller individual. x 3. 
Pygidium short, transversely semielliptical in outline. The axis is convex and 
-has about one-third the width of the shield on its anterior margin. Its sides are 
straight or slightly incurved, scarcely tapering, for about one-half the length of the 
shield. Posteriorly it is broadly rounded and terminates in an elongated ridge 
which extends to, and is confluent with the marginal thickening of the shield. Three 
annulations are distinctly defined and behind these are one or more transverse rows 
of fine tubercles. The pleurz are depressed convex, thickened about the margins. 
There are two distinct pleural ribs, the anterior being deeply sulcate and its two 
divisions uniting to forma single narrow, acute, moderately long spine. The second 
rib is also broadly sulcate, is much smaller than the first and its parts unite out- 
wardly to form a second marginal spine longer than the first. Behind these two 
ribs there are two tubercled spaces extending to the median prolongation of the 
axis. On the margin, besides the first and second pairs of spines, there is a third or 
terminal pair somewhat shorter than the others, and between them and the second 
pair is a small and short accessory pair, making in all eight short, rounded spines. 
On the under side or doublure these are more flattened than above. 
Length of average specimens 4 mm.; anterior width 5 mm. 
