OLENELLUS AND OTHER GENERA OF MESOXACID.E 309 



fig. 21 with fig. 2; fig. 19 with fig. 4; also with the young cephalon 

 of Wanneria halli, as shown on pi. 31. These all prove the close 

 family relationship of the young of Pcrdeumias, Wanneria, and EUip- 

 tocephala. The description of the young cephalon drawn from the 

 Montevallo specimens is as follows : 



Description of cephalon. — Cephalon moderately convex, elongate, 

 semicircular in outline ; bounded by a narrow, wire-like, rounded 

 rim that is continued at the genal angle into a short, slender spine ; 

 posterior border narrow and interrupted toward the genal angle 

 by a short, sharp intergenal spine. No facial sutures are indicated 

 on any of the specimens. Glabella about three-fourths the length 

 of the cephalon, narrow, elongate, and with the frontal lobe about 

 one-third of the total length ; three posterior transverse lobes and 

 an occipital ring are separated by slightly oblique furrows that pene- 

 trate nearly to the center. These three lobes and the posterior lobe 

 or occipital ring are nearly of equal width, and each has a small 

 central elevated node or tubercle at the posterior margin. The 

 occipital ring is separated by a strong furrow from the narrow pos- 

 terior marginal rim of the cephalon. Eye lobes elongate, extending 

 from the large anterior lobe of the glabella to opposite the occipital 

 ring. They arch outward so that the inner m.argin is about the 

 width of the glabella from the outer margin of the glabella. The 

 eye lobes are separated from the anterior lobe of the glabella by a 

 narrow furrow, although, in one crushed specimen, shown by fig. 20, 

 pi. 25, the frontal lobe of the glabella is pushed in by the strong 

 eye lobe ; the space between the outer margin and the glabella and eye 

 lobe is broad, gently convex, and without traces of facial sutures. 



A young specimen [fig. 22] about 2 mm. in length has a narrow 

 occipital ring, three broad glabellar lobes, and with the anterior 

 glabellar lobe almost joined to the eye lobes; the sides of the ceph- 

 alon are rounded in so as to bring the genal angles within a vertical 

 line drawn backward from the outer margin of the eye lobe. The 

 three short lobes of the glabella appear to be extended on each side 

 into srnall lateral lobes that, with the central lobe, give a segmented 

 appearance to the cephalon. This is further increased by the eye 

 lobes and the anterior lobe of the glabella ; the side extension of the 

 posterior lobe of the glabella is continued into large intergenal 

 spines, nearly as long asthe head, that arch outw^ard and the curve 

 inward. In the specimen represented by fig. 21 the tendency of the 

 genal angles to draw in toward the base of the glabella is indicated, 

 6 — w 



